I have attended both USC and UBC so I thought I would weigh in here. NOTE-I am only comparing USC and UBC because I have not attended any other schools.
Academically, the two schools are comparable, both pretty good, so lets leave that out of the discussion.
Now to the important stuff. My take, if you like to ski powder, UBC is your school. Whistler is within 2 hours meaning day trips based on morning snow reports are completely fair game. Also, whistler is absolutely epic on powder days due to its tremendous terrain. When there is no snow, the park is sick, but only when the sun is out, which will not be too often.
If you are a park rat, the choice is USC, no discussion. Mammoth's park is amazing and it is sunny practically every day. Get a schedule with no classes on fridays, join the ski club which will give you access to a house in Mammoth, and skiing three days a week will be the norm for you. I actually ski more now at USC than I did at UBC because of the house (but I had more powder days at UBC because I would go up Whis every time it snowed more than 15cm). Mammoth is sick when it does snow, but the terrain does not compare to whistler.
As for non-skiing wildcard factors, if you want to go to football games, frat parties, get involved on campus, and live the american college dream, go USC. UBC is a giant public school where upper classmen typically live off campus, you can drink at age 19 which means your social life will quickly revolve around bars, and the only sport people care about is NHL hockey. Not a bad thing if you like living a more grown up life, but different than the 'animal house' experience you would get at USC.
The good news is, you can't make a bad decision. The best four years of you life will occur at either school, all you need to do is choose what those best four years will look like.
