It depends on what you like to do when snowboarding (terrain park, cruising on groomers, extreme terrain, etc.) Breckenridge is fun and less expensive than Vail or Aspen. Steamboat is also great, lots of different terrain and fun at night. Crested Butte and Telluride have sick terrain, but if you re not truly and expert then you could be happy at any of the the other mountains. Winter Park is fun but I think the terrain there can be a little boring. So I guess I m recommending Steamboat or Breck! The good thing about Breckenridge is you are in Summit County and therefore close to other mountains like Keystone, Copper, Loveland (which is never very crowded), and Vail in case you want to mix it up.
Really any of them, its Colorado, but a buddy of mine goes out to Breckenridge and has a blast. Theres been a few ski/snowboard videos shot there, so he must be on to something.