Although I've never had the opportunity to visit there, I'd say the Pacific Northwest for all the reasons onesnowyowl mentioned.
I'm from Missouri, and have lived here all my life, mostly in exurbia. Personally, I prefer cold weather to hot, and I abhor humidity above all else, and so the climate here isn't too appealing. Also, I find the major cities here (St. Louis and Kansas City) to be rather generic in most regards. I now actually live in a small college town in rural Missouri, and I find that I prefer that to St. Louis. It's refreshing to be able to walk to most of the places you need to go to, rather than driving for 30 minutes. It's also nice that all the bars here are within 3 blocks of my apartment
.
I've also visited Florida, Colorado, California, much of the east coast, and Wisconsin. I'd probably pick Wisconsin over Missouri, but the others seemed to have too many of their own negatives attached to really make a move worthwhile.
I've read a lot about the Pacific NW, and from what I've determined, it's ideal for me. I'm looking into a trip there on my next Spring Break, and, assuming I like what I see, I hope to land a job up there sometime.