A lot of very good opinions, I started cycling with flat pedals on a MTB. I had used toe clips in Europe when I was a kid (LLOOONNGGG time ago) My first trial with cleats & clipless pedals was a disaster, trying them out in the back yard, not watching what I was doing, springs set too tight, GUESS WHAT?
Yep sprained ankle.
I wouldn't use anything else now. There are many sorts (as said previously) Time (lots of side to side float, no sore knees) Egg beaters (similar but mainly MTB) & SPD Shimano. I have SPD on all my bikes now, some have a flat cage around (as opposed to the spd one side, flat the other) the springs, so you can use them with "street" shoes.
A lot more power, comfortable foot position, and uses some different muscles to give the others a rest now & then.
But... ... it's all down to what you are comfortable with.
Cycling never gets any easier
you just go faster