We are planning the same thing for next December. Right now we are looking at Keystone so that we can use our points via the Concierge collection. To give you an idea, a 3 bdrm condo in the River Run area of Keystone would cost 60 points/night next year the week BEFORE Xmas (Dec 15-22). On the 22 through New Years, the price per night for the 3 bdrm condo goes up to 123/night. So, like one of the other posters said, the week before is relatively inexpensive and the week of xmas is VERY expensive.
From someone who has skiied all of the previous resorts mentioned I would probably opt for the Keystone resort to stay at for several reasons.
1) Conceirge points from DVC and not having to battle with an exchange through II.
2) For a family with kids Keystone has a lot to offer besides skiing with their frozen lake for ice skating, sleigh rides and others.
3) Keystone has a free resort transportation system to its mountain and also Arapahoe and Breck. I can't remember if they still have one to Cooper or Vail.
4) The skiing may not be as good as Breck, Cooper or Vail, but it has been getting better and better through the years. And the other mountains are at most 45 minutes away (Vail), so you can get a summit pass and mountain hop if you will.
5) If you fly into Denver rather than Vail, then I believe it is one of the closest resorts compared to Vail, Breck, Aspen/Snowmass.
6) It just has a great family atmosphere.
If you do not have kids or your kids are older, then maybe a town like Breck or Vail might suit them better. No matter where you stay, as the other posters have mentioned, the other ski towns are great and should not missed. I would definitely plan a day to at least see the other towns if not ski there too.
Anyway, best of luck and I'll see you on the slopes next Dec.
And to 'thelionqueen' my DW and I have been trying forever to find a job out there so that we could join you in your 'magestic state'. Seems like everyone there knows the secret and is keeping it to themselves. I guess we'll just have to settle with retiring out there, so I don't have to look for a job. Now, if I could just get these lottery numbers correct....