I only know Vail, Beaver Creek and more recently Aspen we moved here about six months ago.
Vail has Vail Village and the Lionshead area that are full of restaurants, clubs/bars, and little shops/high-end stores, and has more of the "Ski Village" look and feel to it.
Beaver Creek is more up on the mountain and is more secluded than Vail not as crowded more of laid-back feeling, at the base of the mountain is a town called Avon which has restaurants, stores, and Bob's a little sports bar/restaurant.
Aspen has a really nice downtown area with a lot of the original 1800s buildings and there is still a lot of houses in town from that era too. They have all of the high-end stores downtown, with nice restaurants and bars.
Like others have said Vail and Aspen are going to be crowded and busy that time of year. Aspen seems to be a little more expensive than Vail. I would look into getting an Airbnb, you might be able to save some money and have more space than the hotels. Depending on where you are staying if you are driving up than I would make sure they have parking available and if it is free or not, if you are flying in make sure you have some short of transportation lined up because the airport for Vail/Beaver Creek is about 20-30 minutes away. The Aspen airport is about 15-20 minutes away. They both have shuttles and buses available I would just have a plan for when you get there.
I forgot Snowmass Village its nice up on the mountain kind of reminds me of Beaver Creek.
