Just wanted to toss in a plug for Crank Brothers Eggbeaters. I just switched to them from SPD's, and I'm loving them so far. With my SPD's, I popped out a number of times while applying excessive backpressure during a poorly executed trackstand. It was hard for me to find the right tension to prevent 0 mph crashes but allow backpressure.

On the eggies, it's never a problem. As I'm sure most people know, there is no tension adjustment...the release angle is determined by the position of the cleats. But once you're in, the vertical tension is rock solid. I can pull off all the crappy trackstands that I want now!

That said, I have no experience with clips & straps. I started out clipless on my road bike, and never looked back.