I have a lot of family that live in Seattle (I've never lived there, just visited). It's a great place to visit; I would hate to live there. It's got sort of an older-snobby feel to it. There are a lot of young people living in Seattle, but I just feel like there's a lot of older, snobby people there as well. Sort of drives me nuts. I love college towns and Boulder is a great college town from what I have heard. I'm flying to Colorado in a few hours. I'm not going to Boulder, but I will be driving through it
Personally, I'd say Boulder (even without having ever been there). I might have a biased opinion due to having relatives in Seattle.