I'm not from out West so take what I say with a grain of salt.
It really depends what you want and your skill level.
If you've only skied a few times in your life and are looking for fun, I'd say Breckinridge or Park City are your best bet, most people say they're relatively flat and they both have big park scenes as well.
If you're an advanced skier who's looking for a nice challenging mountain, I'd say Vail, Alta, Jackson Hole, or Squaw. All four have big mountain scenes with Jackson Hole being the most advanced by my standards. Although these lack serious parks, I believe Vail does alright, but as far as I know the other three aren't too advanced in that realm.
For an intermediate resort with great powder and an awesome town, I'd say Steamboat. Not sure on the date, but if you go in February of 2013 you'll be able to catch the Winter Festival they hold in the town. It's really beautiful and the lights and fireworks of the hill are amazing.