Platforms for sure
Depends on what kind of riding you are doing. If you are spinning, then there is an advantage to clipless. If you are chugging up a steep, non-technical hill, then clipless are handy. But just how handy? I find there isn't all that much of a dead zone with platforms. Sure, you loose a little...and if you spinning for a long time, you probably loose too much. But for technical uphill, single tracks and downhill I am a platform convert.
Uphill, you don't loose that much power, but you do loose the psychological confidence that knowing you can pop off your platforms at the very, very last minute. Many times I won't make that last crank effort when I'm in clipless pedals because I know that if it doesn't work, I'm not going to have time to bust loose. So I just don't do it (and the times I do...I fall over).
Downhill, I feel much safer on platforms -- even through rock gardens. I feel better about going for it, because I'm not locked into the bike. Even on pretty severe rocky downhill stuff (I have a hardtail), my feet don't pop off the peddles. I'm standing on the peddles. A couple of weeks ago I was comming down the Downiville Downhill and went over on one of the hairpins. I just rolled down the hill a tad. If I had been locked into those pedals I would have been a gonner, smashing over on my hip and sliding down the trail with a chunk of metal tied to my feet. Same for wheelies...you ain't going to kick off the bike if you're bolted into clipless pedals. And there is no way I would try to pop a wheelie to put my front wheel up over something really big and scarey, then shift forward to try to get my back wheel up over it, if I know that if it doesn't work I'm going to have to win the battle of the eggbeater, or thump over onto my side.
Another disadvantage to clipless is that they build funny habits (my opinion). When you are hopping, for instance, a lot of the hop technique comes from what you do with the handlebars. I know it looks like its done with your feet, but watch the BMXers (who all ride with platforms). With a hop, you pull your front wheel up, then push the bars back down again and the back wheel comes up, and you get a kind of dolphine-like arc...instead of trying to lift the bike with your clipless pedals. You certainly aren't doomed to this sort of thing just because you have clipless pedals...my son rides clipless pedals and does really cools hops over very nasty things...but if you start off hopping and getting air by pulling up on your peddles, I think you don't learn the technique very well. And from what some of my son's friends who can jump up onto picknick tables say -- you never will.
But maybe having big hops like that, or doing technical stuff isn't what you want anyway. If you are mostly on double track fire roads that call for plenty of spinning, then clipless are probably the way to go. But for technical stuff I don't think you loose much from giving up a little upstroke that you probably don't take real advantage of anyway. That's just my two cents.
-M
