I have the following: Shimano LX, Shimano XT, and the SP PD-8. SP PD-8 has the least resistance, lightest, and least chunky looking. Durability wise (such as extended backcountry touring) I would go for Shimano XT. I had the SP PD-8 for over a year now and it works great, very dependable.

Buy them all and find out for yourself.