Regarding crowds, avoid Xmas / New Years, avoid any long weekends, especially the American long weekends. Spring breaks get pretty crazy too. Also the WSSF is busy, but more busy in the village than on the mountains.
Those times are busy, with LONG lift lines, the rest of the season, you have 2 huge mountains available for your pleasure, and lift lines are often non-existent. I have spent many days on Whistler / Blackcomb, where every lift is a direct ski onto (except maybe the first upload)
One exception is Saturdays, they tend to be busy most of the year, and generally I set aside Saturday as a work day, unless it dumps
