We live a south of Denver, but most of our meets are there so I have seen most of the Denver area gyms. Only gym in Centennial is Champions. We were at a meet there in Jan. and have competed against them in the compulsory levels. Nice sized gym. They tend to have more competitive compulsory teams than optional and their compulsory teams are large(number wise). I believe they compete L4(not every gym in the state does).
Probably more gyms in the Parker area. Parker School of Gymnastics comes to mind. Smaller program---not ultra competitive. Have never been to their gym. If you have questions about some of the other gyms, just PM me and I'll look on the list of gyms from the USAG/CO sites. Probably the top gym in metro Denver is Colorado Gymnastics Institute(CGI). Not an overly impressive gym, but a very strong program. Their girls were competitive in every level except L10 this past season( I think they lost a few L10s from the year before). Very good gym for teaching technique----especially beam.