good suggestion tskobo, Nice thing about Aspen is that the airport is close, very close! Steamboat is another option. It can be more costly in terms of lodging than some others in Colorado but again you can fly right in, take the shuttle and not have the added expense of a car. I would not go though if your drving in from denver as rabbit ears pass can be pretty tricky driving.

Last year we went to Park City over Christmas break with our two girls, then 15 and 13. They skiied three days at Deer Valley and one day at Park City resort. They are excellent skiers, and loved Deer Valley. There were indeed crowds but it didn't affect their enjoyment. We took a two bedroom apartment/hotel right by the town lift in Park City. I don't ski, so I was able to drive them every day to the lift at Deer Valley, and then we ate every evening in Park City, which was a great town. This area is very convenient because its a very short drive from Salt Lake City airport. We've also been a few times to Breckenridge, which they also loved, but it is a long drive from Denver airport into the mountains. Both are expensive, but it likely will be expensive most places during Christmas week.

I know you said in the US but Whistler in Canada was my late teen brother's favorite - over Aspen.