T-GunZ, I think there has been pretty decent advice in this thread about Denver neighborhoods so far. It sounds like I am probably in a similar position as your friends (younger middle-aged professional living in Denver with no kids), so hopefully I can give some good advice.
I would urge your friends not to look at any of the suburbs mentioned, as I think that they would be missing out on the great advantages of living in Denver if they move directly to the suburbs. I would also advise against Stapleton, mostly because it just feels like too much of a cookie cutter suburban family community where two professionals without children might feel out of place. I think Stapleton is probably a nice place if you want a suburban family feel inside the Denver city limits, but I don't think it is ideal for two young professionals without children. On the other side of the spectrum, I would probably advise against LoDo because it will probably feel too young for your friends, as the LoDo populace largely consists of young single people who just moved to Denver after college.
I would recommend that your friends look at a neighborhood in Denver where they can get a house in a residential area that is surrounded by a vibrant restaurant and brewery scene. My top recommendations would probably be the Highlands, Washington Park, Uptown, Platte Park, Congress Park, City Park, Sloan's Lake, and Park Hill. All of those neighborhoods are conveniently located to downtown, parks, and other fun parts of town with lots of new restaurants and breweries. I think that they could probably find a cool place to live in any of those neighborhoods. Just be aware that the real estate market in Denver is pretty intense right now with so many people flocking to the coolest city in America, so they will likely have to act quickly if they find a place that they really like.
Let me know if they have any questions about specific neighborhoods or Denver in general.