I'm a bit biased towards the Smokies as I grew up fishing those streams but would say that in general, the two locations are pretty similar. A lot of streams out west have a better nutrient load so people tend to feel like the catching is a lot better since they are catching larger fish more consistently. It all boils down to each person's definition of better.
Generally I feel the fishing is about the same as far as productivity goes if numbers are your only criteria. However, I will also say that there are lots more small streams to be discovered out here in CO that never get fished whereas in the Smokies, the majority of the accessible water is fished fairly hard. People out here tend to gravitate towards the big water of famous rivers and lakes so the small to medium stuff is often overlooked.
Finally, there are lots of reservoirs that produce major spawning runs of big fish, something that is mostly lacking in the southern Appalachians. Lots of the big trout that are caught out here are in conjunction with those runs, or with the extremely nutrient rich tailwaters below some select lakes. If trout is your thing, the Rocky mountain states are probably better, but the variety in Tennessee is much better if you ask me!!! In fact, for variety, I know of few other places I would rather live outside of saltwater options...