double post, but I'll make it useful.
If it's an option and you wanna start really small, start with like Park 101 at Beaver Creek. It's at the top of the mountain, and when you get out of the park the runs are still fun because of the trees and whatnot, and it's steep. Then Zoom Room. I used to love BC because it's pretty empty, but I had one hell of a time last year getting my rythm down for the jump lines in Zoom Room and Bonanza.
Then go to Vail. Their medium and big park are basically integrated like Keystone. Still empty.
Park Lane at Breck is the best park I've ever been to (at least the jumps), but you really pay for it with the crowd and waiting in queue to hit the jumps. God damn, do you wait.
Keystone/I70 is decent and less crowded than Breck, so not a bad option. Their park is huge and there is plenty of stuff to move on to.
Also the problem with Breck and especially Keystone in my opinion, is the transition between smaller rails and bigger, technical rails. Vail has this gray area covered really well. Lots of technical rails, but they aren't huge.