To answer your question:

Speedplay Zeros are the most popular and what I would suggest, especially for fixed-gear use. You can adjust the float range from 0 to 15 degrees. The engagement mechanism is in the cleat, not the pedal. This makes the cleat relatively big and just about impossible to walk on. The float system is amazing, though. It feels like you aren't even connected.

Speedplay has the most sophisticated fit system of any brand. Wedges, extensions, stacks, etc...It's amazing if you take advantage of it.

That being said, Shimano SPD-SL seems to be the predominant pedal on the race scene, especially among sprinters. I use Dura-Ace. I used Speedplay last season. Speedplay seems to be most popular on the road scene.