realskiers

In the Dillon & Silverthorne area (immediately west of the Eisenhower Tunnel) is A-Basin, Keystone and Breckenridge (all Vail resorts).  30 minutes (or a bit less) further west is Copper Mountain.  Another 30-40 minutes farther west is Vail, and another bit west is Beaver Creek (also owned by Vail).  Loveland is back on the other side of the Eisehnower Tunnel (closer to Denver), but most of the places to stay are in the Dillon/Silverthorne area.

Depends a lot on temperatures.  Loveland and A-Basin are the highest, so they keep snow the longest and suffer least from warm weather but are the least "resort like".  Beaver Creek is also pretty high, but they are a drive west from there.  I personally really like Keystone for it's blue slopes, and Breckenridge should be skied one day just to see if you like it or not.  You can buy  multi day passes for the Vail resorts that provide a fair amount of flexibility.  With a 4 day pass, they allow one day at either Vail or Beaver Creek, with 5 days they allow 2 days at Vail/BC.  Of course, any of the days can be used at any combination of A-Basin, Keystone, or Breckenridge and you don't have to ski Vail/BC at all..