To add to RickBravo's reasons for living in Denver:
Oh, wait. That may be a deterrent.
Either way... I've lived in both cities and surrounding suburbs. Seattle - age 5-21, Denver - 22-30 (gasp!). I am not going to break down all the lovely factors for one or the other but will just quickly point out the most obvious differences from my perspective.
Insanely naturally beautiful during the 4 weeks of "summer" where temps rarely hit 80 (and even if they do you'll find chicken teeth quicker than a cloud break). The average Joe on the street is not overly friendly. Great for lovers of coffee, burned out garage band groupies, and those addicted to hemp, keeping up with the Jones' urbane yuppie life. I really do miss being able to satisfy a craving for crab at 10pm by driving a few hours, dropping the pots off in Westport and having steaming, fresh-caught crab to munch on by midnight. But that's about the only thing I miss from Seattle.
Denver: SUNSHINE!! I LOVE having 4 distinct seasons. Sometimes, it's even sunny when it's raining here (don't ask me how). The rain usually comes in torrential, gulley washing downpours - lasts 45 min at most - and you're back to sweet sunshine within the hour. I live right against the foothills so my weather is a bit different than those that live in the high country or on the plains. During winter, I'll get 3-6 inches of snow in a couple hours which will last one or two days tops and by the third day you can wear your shorts and t-shirt. Did I happen to mention I love the weather here?
People: If you can stomach the occasional cowboy (took me a while to build the immunity to it) then the people are more friendly (in general) than up north. Seem to be less self-involved.
Outdoor activites: Where to begin... Snow skiing is some of the best to be had in the world. Whether you're into posh commercialism or small, hidden local's runs you can find skiing to suit your tastes. Watersports (no, not that kind): We're not big on those lake things locally, but within a couple hours driving time you can be at 4-5 substantial lakes/reseviors for all the boating/wakeboarding/skiing/nudity (wait, that's only if you're with me) you can handle. For hiking, camping, hunting, fishing, motorcycle riding, mountain biking, kayaking, hang gliding, rappelling, etc - did you know we've got some damn big mountains here? If you're into jogging, rollerblading, street cycling we've got miles upon miles of bike paths that criss cross the city. You can ride from the furthest eastern edges of the city, through downtown, all the way out to the mountains on any number of bike paths. We have tons of open space parks (excellent for exercising dogs and easy hiking). There's rec centers dotting each suburb, a wide variety of sports league things for softball, hockey, baseball, football, soccer, etc.
Sports: Bronco's football and Avalanche hockey. Need I say more? Probably not but hey, if you're into gangsterball there's the Nuggets, Rockie's baseball, soccer has the Rapids, there's Mammoth lacrosse and some arena football team with a forgetable name. Not bad pricing on any of it either.
Nightlife: I could get graphic but the mod's probably wouldn't let this go up. Let it suffice to say that if I find there to be more fun to be had out there than I have time to explore....
If I've left anything out, or if you need clarification, just let me know.