I'd say AK/BC, if you're looking at purely skiing. Especially if you're having a guided trip and stuff!
Over here in Europe, yeah its fun, and a wicked party, and big mountains that you can do whatever the hell you like on. But you're never guaranteed good snow. You could have a trip, and be skiing on boilerplate for your whole time. Surely in AK with a guide, you're for sure gonna get some rad skiing.
If you're looking for more of an all round experience, Europe. Different people, big parties, resort towns with some history, bit of culture, then head over here.
Either way, you're gonna have one helluva time. Happy 21st anyway!