I've used look road pedals, single and dual sided shimano spd pedals, and most currently crank brothers eggbeaters and acid (same "core" as the eggbeaters, but with a platform around them). Hands down (or would that be foot down? ) The crank brothers eggbeaters have been the easiest to clip in, only shortly behind the acids (which became easier over time, just had to learn the feel of the pedal a bit more).

IMHO, any of the crank brothers pedals are the best out there currently.