Best: Middlebury, Vermont. I stayed in this little town for a couple months and I found a bunch of great trails, and the Trail around Middlebury path has lots of shade and soft paths. Lot of mud, though. I think I lost my shoe in a bog a couple times. It's just a very peaceful place.
Worst: I would have to say Southern California. I'm from the east coast, and something about the air around Yorba Linda just seemed to suck everything out of me, maybe its the dryness. Plus, there's not a wink of grass anywhere, at least that I could find.
Anybody have anything to say on Washington DC?