If you're coming for a few days (3 or 4) go to Whistler. If you're coming for a week or more go to Tahoe. There are soo many different resorts with a ton of terrain you'll never get tired of any of the 3 but if you go to Tahoe you can ski multiple resorts.
I would say wait until about 1or 2 months before you plan to go away to book the trip this way you go wherever the snow is good(look at what happened w/ whistler mid season this past season). The airfare to Tahoe goes down alot in the winter. I bought round trip tickets to tahoe(sacramento,Jet Blue) from NY last FEB. for $185. So if you can pick the time you want to go away in advance but wait to actually book the trip until it gets closer!!!
ive been to all all three pluse many more i would have to say they are all top rated in skiing their, their parks all have a different setup and flow but include thae same amont of technical stuff. if u go to any of them u will not be messing out.
there all really sick..i don't know alot about whisterler personally but it of course has a good reputation. mammoth has the best park but i don't like the lack of trees and wind there. tahoe rules for most choices, pest park in tahoe would be at sierra...just check freeskier