I prefer something with at least a little platform so I have a bigger target and some support. I current use old style Crank Brothers Candy pedals which are quite popular CX pedals because they clear mud well. If you want even more platform Crank Brother Mallet DH racing pedals use the same cleat and have a full platform you can ride in flat shoes for short distances. The new Shimano SPD "Trail" pedals have a bit more platform and Shimano also makes full cage DH pedals if you prefer SPD. Price wise you have to shop around a bit and see what you can find, most of my pedals were on sale or closeouts.