GO CLIPLESS!!! You will never go back.
I was scared to death to try them, but seriously once I switched over, it was the easiest best thing I ever did. Not only are they better from a pedal-efficiency standpoint, but they're safer. When I'm going over rockier terrain, they hold my feet to the pedals so I'm not bouncing all over the place.
They're the best!! Trust me. You'll love 'em. I have the spd pedals that have the metal "cage" around the outside so if I'm cruising w/o my shoes, or if my shoes get too muddy, I can just use them like regular flat pedals.
Fast=Fun!