I use Look pedals because I have had problems with plantar fasciitis in the past, and I have read that for some the SPD pedals are too small to keep the foot stable. BUT others love the SPD pedals and say they are easiest to get in and out of. I find the Looks easy to use.

I also just got Sidi shoes (had Shimano and Specialized before, and they didn't fit well). The Sidis are awesome. You won't have any problem walking short distances in them, say, to a park bench or something while you're on your ride. If there was a reason you would be walking some distance, then you probably would want to go with mountain bike shoes.