I will start by saying that I don't know anything about Boston.
I vote Portland. It's got a similar feel to Ft. Collins but is much cooler. There's a ton of outdoor stuff to do, much of which is similar to the types of outdoor stuff in Ft. Collins, just less of the rugged mountain kind of thing and more trees. They've also got a MUCH larger and more active BF and GLBT community than Ft. Collins.
If the heat/humidity isn't an issue than I'd say Austin. I've heard the food there is pretty good.