There's a confusingly huge amount of information floating around about pedals on the bike. It's easy to listen to people talk about power transfer and pulling up on the pedals and things like that. And most of it's totally wrong.
I thought I'd insert some reality to the situation. I even checked my references!
First things first: If you are riding for the joy of riding and aren't concerned with reaching the maximum amount of speed that your body is capable of, you shouldn't be worrying about pedals. You want plain old flat pedals, maybe one of the bigger ones that provides a wider platform. And whatever shoes you feel like. You don't want toe clips or clipless pedals or powergrips or anything else like that. Keep it simple.
On the other hand, you may want to use something fancier. If you are riding a fixed-gear bike, you need to think about this. Or maybe you just want to ride faster. The right pedals can make an already fast rider go faster and farther. There are two major pedal types, besides the plain old flat pedals:
If you go to Rivendell Cyclery's website, written by famed retro-grouch Grant Petersen, you'll find "The Shoes Ruse," which is pretty much the encyclopedic explanation for why Grant would rather you wear street shoes.
And, you know what? He's pretty much right for average recreational riders. Most average riders are going to be the absolute happiest with a plain old flat pedal. Period. You can wear whatever shoes you feel like wearing, don't have to worry about getting your feet properly clipped in, and don't end up spending much money. You won't notice much difference in efficiency at recreational speeds, distances, and level of effort.
Anything but regular old flat pedals is going to anchor your feet in. This takes skill. Getting in is easy. You'll put your toes in the clip or click-in to your pedals and get going. And then you see a stop light and slow down. Eventually, the bike starts to lean over... but your reflex is to pull your feet up or to the side and you can't. It leans over farther to the side, and you smack into the pavement, still attached to the pedals. In general, this is more likely to happen with an audience.
After one or two falls and some mental reminders, you'll get used to the motions of getting out of your pedals. It becomes part of your muscle memory and you don't even need to think about it. The problem is that you do need to ride often enough to get to that point.
There are some very real benefits to these "advanced" pedals. It's not just style! There's enough of a performance improvement that, if you are interested in riding hard, you will notice. My feet are actually much more comfortable after I got my clipless shoes and pedals. Most forms of bike acrobatics are a little easier to get started. And, even though most urban fixie hipsters use flat pedals, it's much safer for a fixed gear rider to have their feet secured.
Here's where Grant's wrong. Let me explain:
The whole point of toe clips and clipless pedals is to secure the foot against the pedal so that it doesn't move. This means I could pedal my bike with only one foot, both pushing and pulling on the pedals. They used to tell people that being able to push and pull was why people tended to bike faster with toe clips or clipless pedals. People still tell you about this.
On the other hand, there's biomechanical studies (Jorge & Hull 1986, Coyle et al 1991) that show that when an "elite" cyclist is pedaling, they actually pull up less than your average cyclist. From this, you might assume that toe clips are useless, right?
Not necessarily. It pretty much boils down to your muscles being able to work more efficiently. Your brain and nerves are wired towards walking. Pedaling is not a natural thing. If you have your feet fastened to the pedals, it tends to confine your movement so that you can put all of your effort towards spinning and not waste effort keeping your feet on the pedals. This also means that you can pedal at a higher cadence without "bouncing". (Capmal & Vandewalle 1997) The motion most coaches suggest you do is "scraping gum off your shoe". It's funny, because I've tracked that back to an article that explained why you shouldn't be pulling up, except that most folks claim that the advice is how to pull up on the pedals.
Furthermore, they found that they'd get pain from trying to push the pedal where only a small segment of their foot was actually supported, so they put really stiff soles on their shoes and made them specifically oriented towards cycling. Eventually, because they decided that there's a single correct position for maximum power transfer, they'd even put cleats on the bottom of the shoe so that your foot would really lock in place well.
Thus, between the dedicated shoe design and more efficient muscle movements, this is why toe clips, then clipless pedals, were developed. Just because the basic model of "pulling up" is wrong doesn't mean that the whole idea is crap!
In order to understand the wide variety of pedals, it helps to understand the history behind all of the options.
In the beginning, all pedals were nice happy platforms where you'd put your shoe to provide a place for you and the bike to interface, where you would push on the pedals to turn the cranks to rotate the gears and make the bike move.
Eventually, racers started to notice their feet slipping off the pedals. Not all the time, but often enough to be annoying. So they started to put toe clips on the pedals so that they wouldn't slip off. And they also found that if they put a strap in the toe clip, they could get just a little more power. They also started making cleats that would let you increase your retention even further and allow the rider to accurately position their foot.
The problem is that the more you tightened the strap in your toe clip, the better the advantage, but also the greater the risk you couldn't get your foot out of the strap in time. Cleats just made it worse. You'd roll up to a stop and if there wasn't somebody to grab you, you'd land on your side, feet still in the pedals. If you got into an accident, it was unlikely that the pedals would let your feet out, which isn't necessarily the best idea.
Eventually, after a bunch of even more dangerous ideas, including the "Death Cleat" design where you'd have a special cleat on the bottom of your shoe and a clip with a lever that you'd release by hand, a ski-binding company named Look invented "clipless" pedals... which then launched a whole variety of ways to hook your feet into the bike. Because there is no one system that really fits everybody's needs, there's generally a variety of shoes, and several different totally incompatible cleat / pedal systems.
In order for a pedal to work, it needs to contain an axle and a bearing assembly so that it can freely rotate around and enough sealing so that, whenever it gets sprayed with dirt and water and grime, the bearings don't self-destruct on you. The quality of the bearings and seal are a very important consideration. Good pedals will give you years of service without trouble. Bad pedals need elaborate routine maintenance. Well-marketed bad pedals advertise how easy it is to do the routine maintenance, as if it's some sort of a perk. This is mostly a matter of attention to design details and much less a matter of individual features.
In order to mount or remove the pedals, you need a wrenching surface, which is generally a pair of "wrench flats" but some pedals have removed those flats to make the pedals a little bit smaller and lighter and require you to use a hex head on the end.
One side of the pedals is reverse threaded, for roughly the same reason why it's reverse-threaded on older cars. This means that the pedals will get awfully tight on the crank over time and become hard to remove... and eventually cause the crank arms to break... but nobody has cared enough to really solve it properly.
It doesn't matter what kind of pedals you are using, you need to have comfortable feet. I've seen people pedal against a broken pedal where just the axle is pointing out. In general, you will be much more comfortable if the force of your pedaling is spread out over as much of the bottom of the foot as can be accommodated.
Some people really care about the weight. I care about weight, as long as it doesn't come at the expense of durability and doesn't involve me spending absurd amounts of money on the pedals.
You can get resin (plastic or rubber) flat pedals that might get a little slippery in the mud but won't scrape against anything. They also fully support your foot.
Or you can get metal flat pedals, which tend to be able to leave scrape marks on your shin if you walk alongside your bike while wearing shorts. Often times, it's just a metal band or two. These shed mud better. Sometimes there's more metal to them and they'll have metal studs sticking out for better grip.
If you look around, you can find bigger pedals that support your feet even better. Sometimes they even come in fancy shapes. You can also get pedals made from a variety of alloys and painted or coated different colors
Many flat pedals have a pair of holes on them for toe clips. You can get platform pedals which are designed exclusively to take toe-clips, such that the bottom is kind of rounded and they are structured to hang exactly where you want them to.
The goal of a toe clip is to provide a spot for your toe to press against and, potentially, support one or two straps. You can still find them in various shapes and forms, ranging from "half clips" that just keep your shoes positioned, to regular clips.
In theory, you should be able to wear whatever shoes you want with them, but I haven't found this to be true. I had a pair of sneakers that would not fit properly in my toe clips. Between the pedals and the toe-clips, you can also scuff up your shoes pretty good.
On the other hand, they do give you the desired better pedaling dynamics while letting you wear normal shoes. So if you are a police cyclist, you can wear your regular shoes for chasing down suspects or not scuffing up somebody's house. Or you can go touring and hike. And, because urban fixie riders like normal shoes but need better retention, they ought to be using toe clips but don't.
There's a few downsides. Except for a few fancy road-racing setups that clipless pedals largely replaced, you are guaranteed that every time you want to hit the pedals, it's going to require a bit of footwork. The toe clips will naturally hang down, so you will have to put your foot on the pedal, roll it over, and stick your foot inside the clip. Some pedals have little prongs sticking out opposite the toe clip to make this easier. Furthermore, unless you put enough force in to physically break the clip and strap, you will not come loose in a crash. Finally, until you get clipped in, you run the risk of scraping the clips against the ground.
On the other hand, if you use two straps and tighten them really good, your feet won't come loose. Thus, a lot of track riders use that sort of setup because they can track-stand and have somebody help them and having your foot come loose at the cadences they pedal on the track is pretty much a recipe for disaster.
You can do things halfway. There are now half-clips available that don't use any sort of strap but just keep your feet in a better position for pedaling. It's not perfect, but it may be good enough -- they don't let you pull up, but they will still help your muscles move more efficiently. I haven't tried a set yet, but they don't conflict with the present theories.
Pretty much, the way most of them work is that there's a little metal cleat that bolts to your shoe with a special shape that slips into a set of jaws built into the pedal. The jaws will grasp at the cleat but there's enough spring in the system that you can come loose if you pull hard enough. The shape of the cleat and jaws makes it possible for you to twist out of the pedals easily.
Personally, I've found it much easier to use my clipless pedals than toe-clips.
Most designs offer some degree of "float". The exact amount is subject to dispute. If you had cleats with no float, you must get the cleat positioned exactly right or else you will have knee problems. If you have cleats with too much float, you might find yourself getting your knees so far out of alignment, you'll also have knee problems. Furthermore, if you have a loose pedal with lots of float, you end up more muscle effort not twisting your ankles as you pedal. Different designs have different ways to adjust the float or might not let you adjust the float at all. And some folks claim that with their knee issues or whatnot that they need pedals with a lot of float.
Different designs have varying degrees of mud resistance. Mountain bike pedals tend to do a better job at this because it's more of a design requirement. Road pedals tend to get away with much more marginal mud resistance. Cyclocross riders are even pickier than mountain bikers about this because a track needs to have obstacles sufficient to force the rider to dismount, whereas mountain bike trails don't work like that.
The cleat needs to be able to release if you yank it in any direction hard enough (like if you crash) but not release if you are sprinting hard. The cleat is constantly getting ground down whenever you walk and whenever you unclip, so it helps if the more vital surfaces aren't exposed to road grit. Some designs let you adjust how much tension the cleat is gripped with, others do not. Usually, lower-tension grip means that it's a little easier to get unclipped, although less than you'd think. Not having the tension high enough increases the risk you'll pop out at the worst possible moment. Generally beginners feel better with the tension towards the minimum end.
If you watch track sprinters, there's a few ways to modify a standard road clipless pedal to take a strap as an extra measure of safety to prevent coming loose in a sprint. Most everybody else prefers to be able to unclip if necessary.
The pedals and cleats in your shoes are exposed to road grime and get worn down over time. The cleat wears first, which requires you to tighten the tension (if it's adjustable) and eventually replace the cleat because the tension is at max. After that, the pedal wears out.
The first pedals were oriented towards road racing, so there's a big metal cleat under your toes, as hard of a sole as possible, and the whole works is designed to be lightweight. The problem is that you look really silly when you try to get off the bike and walk for a bit. The metal clanks on the floor (and may damage it) and you don't have much traction. More recent designs oriented towards mountain bikes will let you walk in your shoes because the cleat is recessed. They even make shoes that are a little flexible so that you can have an easier time walking. If there's a recessed cleat, they tend to call them "Mountain bike" shoes and pedals, if there isn't, they tend to call them "Road" shoes and pedals. Furthermore, most "Road" pedals can only let you clip in on one side, whereas "Mountain" pedals let you clip in from either side.
There's actually three sets of hole patterns that shoes can use, which may mean that your "road" shoes can't work with your "mountain" pedals and cleat and very likely means that your "mountain" shoes will fail to work with your "road" pedals and cleat. Furthermore, if you are using an especially unusual combination of pedal, cleat, and shoe, you might discover that everything doesn't quite fit.
Road pedals tend to be lighter and most of the time they are single-sided with a significantly larger cleat, although they are usually designed such that the pedals will fall in a ready-to-clip-in position. Road bikers tend to think these will let them go faster, which I'm not totally convinced of. However, there's no room for a recessed cleat, so they are not great on a polished concrete floor. They also tend to be lighter weight as well.
Other than the name and potentially some degree of efficiency, there is no reason why you can't use mountain pedals and shoes on a road bike or road pedals and shoes on a mountain bike. Marketing likes to keep these distinctions from blurring because that way they can sell more hardware.
For most cyclists, road or mountain, the mountain bike styled pedals and shoes make a lot of sense. The cleat is recessed, so the shoes are a little more friendly to walking. It's a clear improvement over both toe clips and platform pedals, plus most mountain pedals have two or four clamps, which means that you just put your foot down and clip in.
There's a wide range in price of bike shoes and a bunch of different styles. In theory, shoes are supposed to last for quite a long time... but some folks I know have spent a lot of money on shoes that didn't last long at all. Most of the time, they tend to look vaguely bike-shoes-esque, but sometimes you can find ones that look a little more like sneakers. Plus there are cycling sandals, which appeal to some folks.
The design goal of bike shoes is a fairly stiff saddle so you don't get hot-spots, to be breathable enough to let sweat out, and to securely hold your foot in place. This will feel awfully comfortable while biking, like you are strapped into a giant pedal. You won't feel comfortable jogging in bike shoes, however. Mountain bike shoes will have a little flex and recessed cleats so that you could run in them (most notably the uphill run-ups on cyclocross races) but you still won't be comfortable. I've tried even more sneaker-like shoes and even they weren't something you could wear all the time.
One important advantage of bike shoes that you shouldn't give up is the ability to not have your shoelaces caught in the gears. Some of them have shoelaces with a flap to hold them in place. My shoes have two velcro straps and a ratchet and I much prefer that.
Fit is very important, so you really need to try shoes on. Higher-end shoes come in different widths to make it easier to fit. Some of the highest end shoes can be put in an oven and be molded around your foot. The materials are often times different, with carbon fiber soles costing more but being lighter and thinner and stiffer.
You can get pedals with a grip on one side and a normal pedal on the other side. The problem is that they tend to be weighted so that one side tends to be the side facing up, which either means that you have to rotate the pedal while going clipless or while not going clipless, which pretty much depends on the pedal. I've tried a set and I hated every second of using them.
You can also get pedals that are double sided but have a cage surrounding the pedal. This gives you better utility while riding partially clipped out, but doesn't really help too much for biking with street shoes. The problem is that the pop-up mechanism still put a lot of pressure against the soles of my sneakers, which leads me to suspect that if you need to ride a mile or two on street shoes, it probably doesn't matter.
You can even get shoes that are designed be flexible to make walking easier. The problem is that the bike shoe is stiff for a very good reason. Regular mountain bike and cyclocross shoes are about as flexible as you'd want them to be before they stop being useful as bike shoes. I did try some of the pairs and, while they were a little more normal-looking and walkable than my bike shoes, they weren't impressively sneaker-ish.
I did discover that Speedplay pedals, which I'm not especially fond of, have a neat plastic cage that snaps around their double-sided pedals to turn them into a normal double-sided flat pedal. Most of the rest of the adapters to add platforms to clipless pedals are only one-sided.
That being said, it's best to pick a path. Either go clipless or don't. Either get bike shoes or sneakers. If you need to bike a mile or less, you can usually pedal on street shoes with clipless pedals and, even though it's far from optimal, it's good enough. Or have one bike that has normal pedals and one bike that's got clipless pedals. Eventually, I got a pair of dress shoes that were gathering dust in my closet and left them at work and both of my bikes have clipless pedals.
I tend to like the Shimano SPD system. This is largely because it's sold everywhere, doesn't cost that much, is decently sturdy, and works well. I've got a PD-M424, which is pretty much a resin cage around a cleat on my mountain bike. The big benefit to the resin cage is that it still offers a lot of support if you aren't totally clipped in. I heard a lot of people gripe about how gnasty the resin part looks over time, but it doesn't bother me that much. I've got a PD-M540 on my road bike, which has no cage, because it's a little lighter and sleeker and the cases where I'd be biking partially-clipped-in only happen off-road.
There are a few different cleat types for the SPD pedal. The first set are multi-release, such that you can twist in most any angle or direction and if you do it hard enough, you'll pop out. The other set are standard cleats, which require you to twist in one particular direction to clip out (but if you yank hard enough or crash, they'll still release). Everybody says that you should use the multi-release type starting out, but I wanted to bunny-hop and that's not so good of an idea on the multi-release cleats, so I gritted my teeth and found the standard ones aren't that bad at all.
I've got Sidi shoes. So far, they seem to be great shoes for the money. Decently sturdy, extremely comfortable, and most of the stuff that might break on you is easy enough to replace. I see a lot of riders with them.
One thing to be extremely careful about is the cleat bolts. See, if you walk on gravel, you have a pretty high risk of having a rock stuck in the cleat bolt and won't be able to remove the cleat without a LOT of effort. If your cleat bolts are loose, the cleat will shift and make it really hard to unclip. If one of the cleat bolts comes all of the way out, you won't be able to unclip at all.
Coyle EF, Feltner ME, Kautz SA, Hamilton Mt, Montain SJ, Naylor AM, Abraham LD and Petrek GW, "Physiological and biomechanical factors associated with elite endurance cycling performance", Medicine and Science in Sports and Exercise. Vol 23 No 1: 93 â 107, 1990
Jorge M and Hull M, "Analysis of EMG measurements during bicycle pedaling", Journal of Biomechanics. 19: 683-694, 1986
Capmal S and Vandewalle H, "Torque-velocity relationship during cycle ergometer sprints with and without toe clips", European Journal of Applied Physiology. 76: 375-379, 1997