You just described Banff perfectly.  There probably isn't anywhere in North America where the snow is as light and dry as it is in the Banff region.  Relative humidity in the winter is typically between 15 and 20 percent, and the joke is you can fall in the snow all day and never get wet.  The statistics for the area are that it gets 330 days of sunshine annually.

Snowfall is a hard thing to judge or make predictions about, and you can't make generalizations about regions because snowfall can vary dramatically between areas that are as little as 10 miles apart, and quibbling about a few feet of difference in average snowfall is meaningless.  Every ski area will have it's own annual snowfall statistic.  If you're looking for a number, what I can tell you about Banff is that the average annual snowfall for the Sunshine Village ski resort in Banff is 33 feet compared to 28 feet for Vail.  What difference will that make to a 10 day day ski trip?  Probably nothing.

As far as partying, I guess it depends on what you want to do.  I haven't partied at Breckinridge, so I can't comment about that, but the difference between Banff and Vail is that Vail is a manufactured, glitzy resort while Banff is authentic town, similar to Aspen.  They both have their pros and cons, and both will offer ample things to do in the evening.  Banff will tend to be a bit rowdier, in my mind, because the locals (seasonal workers) will party it up more, whereas in Vail the nightlife will be primarily tourist driven.

Another factor to consider is cost.  Skiing Banff for 10 days will cost you far less than going to a destination resort in the U.S.  The winter season is considered low season in Banff, so hotel rates are at their lowest for the year (with the exception of the Christmas/New Year period).  Everything else will be less expensive as well (lift tickets, food & drinks), and in addition you will get about a 12% bonus due to the exchange on the dollar.  Getting a multi-day lift pass at Vail, for example will work out to $83/day U.S. compared to $58/day U.S. for a multi-mountain pass in Banff that give you access to skiing at three different resorts.  Just something to think about.