I ride Crank Bros. Eggbeaters, super light, easy to clip in, you dont come out of them, and they clear mud with ease. I ride singletrack and nothing else though.
Platforms are used a lot in freeride and downhill
Clipless pedals are used in XC and Trail but it all comes down to personal preference. I like clipless because my feet dont slip off the pedals and you can really pedal hard and stay in control of the cranks.