Gonna agree with two of the posts here. I went o Val Thorens two years ago and that was really good but hands down the best place for partying i have been (full stop, not just ski resorts) is Pas De La Casa in Andorra.
That place is mental...and cheap as chips too!! Whole country ios duty free and its typically european in that they dont measure the spirits! got a bottle of vodka the first night for about £2!!
I dont think id be able to handle going back tehre again tho, that was when i was about 20, most of my friends were so hungover they'd be throwing up on the slopes next day lol! Funny times.