I've used shimano 636's and mallets for DH.
Both are good pedals, but the shimano enagement is not quite as quick as the crank bros. Shimano's you have to do the "slide forwards, click down manouver, the mallets, you just mash your cleat into the spindles. I've heard reports of people breaking the arms on mallets, 636's are bombproof. I've still got my old set kicking around somewhere from like 1998 and they still work, and have never had a service.
The Crank Bro's pedals are better finished, but both are pretty good.