My advice is to buy Shimano M520 pedals and mountain shoes unless you constantly ride in the mud. I've used both Crank Brothers pedals (Eggbeater, Candy) and Shimano SPD pedals. Shimano pedals have adjustable release tension and require much less heel twist to release than Crank Brothers pedals. In addition, the Shimano SH56 multi-release cleat makes unclipping even easier than with the standard cleat.

Buy Crank Brothers pedals if you need lots of float to keep your knees happy, or you often ride in muddy conditions. Despite all their supposed improvements, Shimano SPD pedals still aren't great at clearing mud.