I agree with Ranchero regarding the cloudbase at Whistler, but when the weather is clear, Whistler/Blackcomb has to be in the top 3 to 5 of a world list.
I would rate both Breckenridge and Vail above Whistler, partly because of the range and variety, but also the consistency of conditions.
My personal favourite above all others is Arapahoe Basin, it is challenging, and high. Also scenic in only a way that an American cowboy and indian resort could be. However, I can see that it would not be a favourite for many.
~ is my perception. :wink: