i went to vail keystone and breck two weeks ago
vail has the best back country, i didnt really like the park. they have 7 bowls and is really sweet
keystone- shit load ammount of rails and well maintained jumps, good town, there lifts are not long waits
Breck- Not too good for beginners or descent riders. the jumps are breath taking but they dont groum the park enought to have enough speed to do anything, break has an insane peak and is very tiring