I'm a spd pedal girl. Give me shimano 959's anytime and I'll be happy. But different people will swear by different pedals. My brother loves his time atac carbons. He swears that they shed mud beautifully.
Some people say that egg beaters are the way to go, that they shed mud better than spd pedals. I'm not sure that is so true. If you have to ride in terrible enough conditions, mud sticks to everything. This year my teammate and I raced in one of the most awful, rainy, miserable mountain bike races ever. She cursed her eggbeaters and I cursed my spd's.
While I'm pretty new to cross, I'd say you want a pedal in which you can easily stand on for dismounts and easily clip into for mounting your bike. Mud shedding pedals would be a bonus...if there is such a thing. But, the pedals that would work the best, are the ones your most comfortable with for CX (IMO).