Last year it was busy on weekends almost all winter. The last two weeks of December and march 10-25 or so sucked for crowds. during the week was pretty dead nov 15- dec 20 and Jan 2- march 10.
Typically the crowd thinned out a lot after 12 and even more after 2. Beaver creek was the same just on smaller scale..... If you have to park in vail you should get here early and park on the west vail north frontage road and grab the red or green bus line to town... Like a 10 minute bus ride but saves you $25