I can't tell you much about the SW route, but the one up to Cheyenne and over I'm assuming cruises up I-25. Not a very exciting drive, but you'll see most of plains Colorado. Traffic shouldn't be too bad, save for around Denver, and you've got 75-ish speed limits most of the way. I'd give the SW drive a try though, would be a lot more interesting, although I don't think you'd hit much of the Rocky Mountains that route.
