For learning:
SPD style. The adjustable tension is great for beginners.
For once you're used to clipless: Probably Time Atacs.
I use crank brothers. I'd probably use Times because of all the issues I've heard of with CB, except I like having the same system on both of my bikes, and bare eggbeaters really can't be beat for on and off the bike (cyclocross). If I didn't race cross or could afford a second set of nice shoes I'd have ATACs on the mountain bike.