The last time I looked at this sort of thing, Denver had two problems. One, if you rent at DIA there is (or at least was) a very substantial airport rental surcharge that was going to add about $100 to a weeks rental (they gotta pay for the airport somehow!). I rented my car downtown to avoid it, but that's a hassle.. The second problem is traffic. Getting through Denver and down I-25 can be a pain if you're timing is bad. I have given up on Denver as a gateway to the ng.
My suggestion would be to fly into Albuquerque and drive from there. Three hours to Chama. Then go to Durango, Georgetown, CRRM, Caboose Hobbies, back to Chama one more time (I'm prejudice of course), and back to ABQ. Colorado Springs also works pretty well. I also use Durango frequently, but it's not worth it if you're doing the circle trip.