I agree with what's been posted already. Christmas can have great snow some years and not so great on other years. This past Christmas 2004 was not so great. It actually started dumping a few days after the holidays, but up to that point the cover was pretty light. By February, the entire mountain is covered and you should hope for a few dumps while you're here.
All things relative, Christmas/New Years and Presidents weeks are the busiest at the Beav, but it's not hard to escape the crowds once you get up Chair 6. Whenever you choose to come, you'll have a great time at Beaver Creek.