I've used the Heavenly to Kirkwood shuttle, and it is easy and cheap. One downside is that it leaves the same time every day, so on a powder day the longer drive time comes out of your ski day instead of your sleeping time.
For the OP's question -- what about the smaller places like China Peak or Donner Ski Ranch? I dont know exactly where they are, but it seems they might be less crowdwd at Xmas. Anybody know?