My best advice for you would be to give the fields a call around mid week and find out what kind of turnout they are expecting. That would give you the best idea of where the most people are/type of people you are looking to play with.
American Paintball Coliseum - (303) 298-8573
Blitz Paintball - (303) 337-7109
Dynamic paintball - (303) 799-9911
Paintball Adventures - (303) 762-6160
There are a few others around the area that I haven't listed but those are the bigger fields around.
Mile High Saints!
Colorado Crash Paintball!