Definitely go with the 540s if you go Shimano. The 520s are a cheaper version and I have seen them grenade after hitting rocks. If you go Crank Bros, I recommend the Candy SLs or I think the new Candy 3s. Those two would be the most XC worth in my opinion. I have EggBeaters to, but find the lack of a "platform" annoying for when I want to keep a foot unclipped.
I started on SPDs and went to Time... will never go back; i like the feel much better. And the platforms work better than my previous shimano pedals that had cages. I don't trail ride with the flats, but i do ride around the neighborhood and the shimano pedals just didn't do it for me.