Portland is number 8 (out of 30), but what I find fascinating is that it is ranked higher among republicans than among democrats. Strange that, for a city that has such a liberal reputation. However, when the question is asked of self-reported conservatives and liberals, liberals rank Portland higher.
The fact that Denver is ranked number one suggests that people rate climate and outdoor recreation very high - which is true when the questions about what is important are asked. So Portland suffers from the former and is good for the latter. A good place to raise children is most important and we aren't so good about education, so that hurts.
A final interesting aspect is that cost of living is a very small factor. It seems like people want to live in nice places, and will figure out how to make it work.
The very fact that this survey exists (and the interesting tidbit that about one in four respondents don't consider the place in which they currently live the place "in their heart") speaks to the fact that we are an incredibly mobile society and are willing to consider living anywhere.
My house in Denver was a few blocks from where this picture was taken (The Denver Museum of Science and Nature) and I can confirm that Denver is a perfectly nice place to live, but does not hold a candle to Portland so don't be seduced by the 310 days of sunshine, the great skiing, the professional sports, the cool art museum, the many breweries, the Rocky Mountians...
Seriously, my main complaint about Denver was that lack of a 'there' there. It seemed to me a city without a soul. I once read that Denver is the number one test market for chain restaurants - to me that said it all. In other words, Denver was not "in my heart." But though people in Portland are pretty zealous about what a great place they live in, Denverites are even more so, they have no doubt that they live in the best city in the US.