hey coops - this is one of those neverending debates that i'm sure everyone has an opinion on, but i'll chime in with my two cents. there are definitely benefits to both: look pedals (and road shoes) have a stiffer sole, and the wider platform of the cleat gives you more efficient power transfer to the pedals. on the other hand, spd pedals (and mountain shoes) are easy to get dirt out of if you're mountain biking, and they allow for easier walking off the bike. having tried both, i settled on spd because of the walking reason. with my spd cleats and mountain bike shoes, i can walk around with no problem, and honestly i haven't found that the pedaling experience is any different than with looks.
that's just my opinion - i'd love to hear what other people think!
I would have to agree with Leah. SPD's are easier to walk in. Look cleats are tougher to walk in. Just be careful walking down your first flight of stairs in biking shoes LOL. Nothing like falling down a flight of stairs for the first time with my bike also falling right behind me.