Ironically Snowmass and Sun Peaks have a lot in common but are also vastly different.
Both are known for long wide intermediate runs, sunshine, and an absence of hard charging new schoolers.
Both have great variety and some pretty decent black diamond skiing.
Both are huge. Snowmass has over 4400 vertical feet and Sun Peaks has 4270 skiable acres, tied with Lake Louise as the second largest in Canada. Snowmass is not crowded but by comparison, Sun Peaks is even less crowded....almost empty. In fact after the Xmas season is over the 325,000 annual skier visits on 4270 acres means that it is literally "acres per skier", not skiers per acre..
However, It is hard to beat the 4 mountains of Aspen for variety and size.
For more info on Sun Peaks, click on my unofficial guide below. The guide is overdue for and upgrade with the biggest changes over the past few years being the on going cutting of black diamond runs on West Morrisey and the Gil's Hill hike-to area is still hike-to but is now in bounds.
IMO if costs are not a major consideration, then Aspen wins out. But the depressed Canadian dollar makes skiing in Canada a lot more affordable than US resorts with only gasoline (due to very high gas tax) being more expensive in Canada than the USA. Food, accommodation, lift tickets and ski equipment are all cheaper in Canada than the US.
A half price lift ticket for Aspen is $70US and is thus more expensive than a full price Sun Peaks day ticket at $90.30CDN, tax included.
An adult season pass for SP if purchased last May or June was $749CDN + tax and is equal to the price of about 9 days of lift tickets. It allows 50% off day tickets at Whistler and 25% off lift tickets at many other Western Canada resorts.
One other consideration for skiing in Canada is that the lower elevation means that there will be no need to get acclimatized to high altitude.