Terrain, parking and atmosphere
The snow is the least of the county together with A-basin
Keystone is a very nice resort, good terrain, and good service. Conditions might not be the best in the county, since it is one of the resorts that gets the least snow in this area, so you are better on going after January 15 or so. My experience here is always good, you can escape crowds by going to the back and staying there. this is the only resort that has night skiing so you can take advantage of that. the layout is much better than Breck and easier to park. They have good terrain for everyone and some great parks.
That said, there is no comparison to Vail. RIDE VAIL, it will be the best experience of your life. Then after Vail try all other resorts in the area and judge by yourself.