Ah-ha! A Colorado question I can answer!
The closest, cheapest, and non-crowded option is A-basin. However, it is pretty small and might not be the most fun. Breckenridge and Keystone are great – a lot of options, varying degrees of difficulty, and they are not too much further than A-basin. They are a bit more expensive though. Vail is a half-hour to hour (depending on traffic) further than the others, and will likely be the most crowded place of them all. But, it is crowded for a reason. It is a beautiful mountain with many types of terrain, bowls, and parks. If you plan on staying up there for a few days then Vail is your best bet, because the town is amazing, with lots of activities and places to eat & stay. Vail will be very expensive.
Beaver Creek is the most expensive and least crowded of them all. It is pretty close to Vail, so most people go there instead of paying more for Beaver Creek. The lack of people make Beaver Creek one of the best places to go – wide open runs with similar conditions to Vail. The best day of snowboarding I’ve ever had was at Beaver Creek.
Hope that helps.