First of all, this has been discussed many many times already.  Just use the searchbar and you won't have to make a thread next time.  I think there are a lot of good threads in the Colorado regional forum.
Second, they both have great parks with their own perks.  Keystone has a pretty exclusive lift, lots of rails, and some good jumps.  Breck has a ton of amazing jumps, a fantastic pipe, and they take great care of their features.