Having skiied at a lot of the places mentioned, if you want both a good mountain to learn on plus a nice town for apres-ski, I'd recommend the following:

Vail, CO
Deer Valley, UT
Aspen, CO (ski Buttermilk as mentioned or Snowmass)

The only downside of flying into Eagle-Vail vs DEN is the flights aren't as frequent. I've flown into both, though, so whatever works for your price & schedule. Obviously Salt Lake City is airport for Deer Valley. Aspen airport can be dicey getting in/out of due to proximity of mountains, weather, runway.

I love Whistler, but you should be a better skiier for the reasons mentioned before going there.

Can't remember if your post said Dec/Jan or Jan/Feb as options. Dec prices are decent (hotel & lift tickets) up until the 15th-17th timeframe, then they switch into 'high season' through mid-April. All resorts are crowded during Xmas holidays. Most resorts are actually not that crowded in Jan once the holiday season is over (Martin Luther King weekend excepted). Prez Weekend in Feb is also very busy.

Have fun. Cheers. Sharon