I can't say much on Washington, but I grew up in Boulder and know several people in geo grad school there. Boulder is a fun quirky place (although it's becoming less quirky as it continues to gentrify and yuppie-fy). You will find some of the best mexican food, vegetarian food, beer, etc in and around Boulder. Definitely a foodie paradise. The weather is indeed pretty darn perfect, although it practically never rains, which bothered me at times but if you're sick of rain that's a plus. Boulder's proximity to national research institutes is also pretty sweet. There's NCAR, NOAA, NIST, GSA headquarters, USGS offices, plus everything at CU and bunches I probably forgot. Tons of culture and stuff to do, super environmentally friendly, very very liberal, generally happy place. Almost every possible outdoor activity is practically in your backyard or a very short drive/bike ride away.
Hmm, some cons on Boulder off the top of my head include:
Pretty high cost of living. Housing prices and rental rates are pretty steep, but probably more reasonable around the university and further south (I lived in north/central Boulder).
entitled yuppies and trust fund babies everywhere (plenty of wonderful people too)
lots and lots of weed everywhere (could be a pro or a con depending on your perspective...)
I'm happy to answer any other Boulder related questions
Contrats! Good Luck!!!