Geez Louise, I wrote that going on fourteen years ago!
Still stand by that view, and I agree with what the tandem guy says too.
Re taking over, you just have to go through unclipping a lot and it becomes second nature.
Can't believe I've been using spd since 91 or 92.
Hope you adapt well, if you used clips like a lot of us did, it shouldn't be a big adoption

A couple of thoughts and no answers. 1) shoe fit rules! If you have "generic" feet, in other words, most popular shoes work for you, your options are open. If your feet are further from norm, you may well find that such and such brand works best for you, perhaps by a wide margin. (For me, it is the Lake shoes.) And that depending on what shoes that manufacturer offers (in fits that work for you), that might drive your choices to the 2-bolt (Shimano SPD and others) pattern or the 3-bolt (LOOK and others) shoes.

Starting from scratch, you can learn to ride any of these systems. Dialed in, there is very little efficiency or power loss with any of the good systems. World championships have been won with nearly all of them. Now, some people need more float. And there are a few that cannot handle any float. Like shoe fit, these can be driving forces for some. (I'm in the no-float category.)

So my advice - try on shoes! Look for the ones that make your feet say "ahhh!". Then start with the most common of the pedal types for that bolt pattern. 2-bolt, I'd go double sided SPD pedals. 3-bolt, SPD-SL or LOOK Keo. (I started on LOOK Delta compatibles before Keo existed and never switched. Not needing or wanting float; there's never been a reason for me to "upgrade" at real expense to pedals and clears that do exactly the same thing.)

Now, ride 'em. Take notes - on foot comfort. Could your cleat placement be better? (Most cleats can be slid forward and back and to the sides as well as rotated. Forward and back changes your pedaling, Side to side may make a difference to your knees. Rotation can make a big difference to knees. Make small changes, ride and take notes. This is a big-time learning process. For most if us, the answer wasn't given overnight. Don't feel locked in to a system that just isn't panning out. Talk to others. Listen. (And keep in mind that we all have strong opinions here!)

Oops! A fairly well written answer to a 14 year old OP!

Oh I hate that, never even looked. Necropost,

All really good pointers that will be a help to this new person new to clipless, so that's okay as it might help them.

For MTBs , Shimano SPD and for road bikes Look Keo or Shimano SPD SL

For those of us who don't race and don't ride on the highest or near highest level, it all comes down to if you need to walk in those biking shoes, and walking here doesn't mean any long distance but even just ten, twenty feet, or indoors on just about any surface.

Another factor is a fashion thing, if you mix with road bikers and would mind them looking down on your pedal choice. If you are the type who wants to belong, do things the way they are supposed to be done, then go for SPD-SL

Bottom line is, either choice won't make you faster on the bike (or only marginally faster to a point where it doesn't mater), it is all about what one wants apart from that.

I have two shoe pairs, those that I use for summer riding can mount either cleat type (I use them with SPD cleats) and those (because they are universal) I can't walk in them.
The other pair for spring, fall riding as they are warmer type, have also normal sole and so have only SPD cleat mount and can be walked in fairly reasonably. I only mention this because I know how it with both shoe types, road of MTB style.

Last point, get double sided pedals (if choosing SPD). Single sided might look more in line with road bike as pointed out above, but are PITA

Shimano ED500 SPD Dual Sided with adjustable tension.
I liked them so much, I have them on my endurance bike as well.
These are for touring and currently $48 on ebay.

Fixed that for you 😁

That is what the Mrs. has for our tandem. She especially likes the recessed cleat in the shows to walk into a restaurant normally, not like her dorky husband. I ride Look Keo because they are on all my bikes and I don't want a separate pair of shoes for every bike.

I have three systems for 6 bikes. Half my bikes are fix gears, I will only ride traditional slotted cleats with those. (The cleats where you fall over if you forget to loosen the buckles. And just about the only system where your foot stays on the pedal if you pull a cleat out at 200+ RPM going downhill.) My two good geared bikes get LOOK Delta compatibles. The black no-float cleats. (Float is a knee killer for me.) My townie/occasional not serious gravel/farmers market bike gets double-sided SPDs with the cleats set to max toe-in and near max release force to get as close to no-float as possible.

This does make for a lot of shoes. And sometimes needing to go back inside to get the right shoes for the bike I am about to ride!

I'm not sure I can answer your question. But, I'll give you my experience. I've been cycling for over 40 yrs. Probably 90% road and 10% cyclo-cross. I started with cages and have tried several clipless systems. About 25 yrs ago I discovered Speedplay Zero. I've never gone back. I also use Speedplay Frogs on the rail-trail. They have been discontinued but I have several sets squirreled away. We are recreational riders so a 25 gram weight difference or a 5 watt savings are meaningless. I think you have to try different systems, if you can, and see what works for you.

So I installed the cleats on my shoes, and just happened to have the right pedal turn with the cleat side up on a recent ride and I accidentally clipped in on the right. SO I rode like that for a few hundred yards, and as we were approaching a light, I moved the right heel outward, and was easily out of the pedal. Accidentally clicked in again a few minutes later. No big deal. But I'm rather bow legged, and the left shoe cleat placement has been a lot of trial and error. My knee was telling me it wasn't right in seconds, and it had taken a lot of effort to get that left foot clicked in. I now have it almost OK. Tomorrow's ride will tell. In the mean time, I'm clicked in on the right when there's a long stretch in front of me with no major hills or intersections. For a a couple of minutes there, yesterday, I was thinking of re-installing my toe cages, because my foot needs the ability to move, but in fact, I might get there with both feet.

I'm one of the proud weirdo freds who use MTB pedals on road bikes.

I use Speedplay Frogs on my road bikes and they are better than Shimano MTB pedals, IMO. I started with Frogs in 2014 and used them ever since. I use Shimano MTB (XTR M9100) on my hardtail 29er mountain bike... and they are good pedals, but not as amazing as the Frogs. It's a shame Speedplay was bought out by Wahoo... and Wahoo didn't continue the Frog line. Frogs are simplistic, with a brilliant design. Super easy to clip in and clip out, extremely durable, easy to maintain, double-sided and light weight. Perfect pedals that allow me to wear MTB shoes, so I can walk around off the bike with comfort and ease.