I'm in for this, Chuck. We need to hit the CA stuff one year/trip and then the CO stuff, too. The Independence trail system, Carnage Canyon, Billings Canyon and Holy Cross are supposed to be awesome.
I moved from western Colorado (Grand Junction) to GA 5 years ago, and did all the hard core rockcrawling stuff while there.
Beyond doubt the best rockcrawling anywhere is JV. Ya can spend a week there and still not do all the trails.
Of the CO trails you have mentioned above the best is the Independence Trail system, although it is rather short. Billings Canyon and Holy Cross are ok but not that tough. Absolutely the best rockcrawling in CO are the trails near Montrose. Another great trail system is near Rangely. If I were to rank CO trails, it would look something like this:
Montrose and Rangely are tied in my opinion and a distant 1st/2nd to the other trails.
Independence
Billings
21 road
Holy Cross
I never got around to doing Carnage Canyon, but from what friends told me it ranks in there with 21 road and Billings.
Just my 2 cents worth.