I choose Crank Brothers EggBeaters these days. Been riding on SPDs for 10 years prior to that, and they're fine too, just heavier and worse in mud. Time ATACs fall halfway between SPD and CrankBros, being medium weight and good in the mud.
Re: Speedplay -- One time I swapped shoes and bikes with a friend who used Speedplay frogs, and I liked them a lot. Engagement is easy. The float massive and COMPLETELY free, to the point that it feels like you're standing on ice cubes. Disengagement is a little vague if you're used to a solid click, but it's not a bad thing. The only drawback to Speedplays is that the cleats are a bit complex and vulnerable to getting smashed if you dismount and run on rocks.
Caveat: I have never felt the need for a big platform. If you like to ride unclipped with your shoe just resting on top of the pedal, don't take my advice.