Well, we are just back from Colorado to our home in NE Texas.
In fact we've made that journey many, many times.
Here is a good mix of US highways and Interstates: We go up to Paris, TX to pick up US 82 to Wichita Falls, then US 287 to Amarillo. Forget the numbers but US highways to Dumas and Dalhart and on to Raton, NM.
At Raton we join I-25 which takes us north into Colorado. No good alternative US highways and an excellent route. Depending on where are headed in Colorado we use US and state highways. Just to give an example, Colorado 69 from Walsenburg to junction with US 50 to Salida, Buena Vista, Leadville. OR continue on US 50 to Gunnison.
So the best route, in my opinion, is a mix of state, US, and Interstate highways, not based on designation but on destination.
