The Allentown neighborhood of Buffalo is actually pretty decent (nice bars, tattoo parlors, shops, etc.), but the rest of the city is pretty much just a giant shithole. I lived in a southern suburb there for a couple years and that was pretty much the only area of the city proper I liked. I guess that's to be expected from a town that went from a population of 2.2 million people down to 900k though (half the city is empty and most of the old industry is crumbling).
But anyways, best would probably be Vienna, Salzburg, or Geneva if I'm going to go international. Domestic is kind of hard because there are plenty of things to appreciate in a lot of cities: Philly has a fun nightlife and great history...dunno though, most of the larger cities I've been to are enjoyable if you have the right guide. Probably go with Savannah if I were to choose a southern city. SF is nice but all the hippies get on my nerves.
Worst is a tossup between Detroit, Buffalo, Duluth, and Cleveland domestically...they're all crumbling but have some minor charm if you find the right area. Foreign I'd have to go with Johannesburg, SA even though I had a fucking amazing time there. If you're well off and white it's great and there's tons of shit to do, but if you're poor and black you probably live in a trash filled shanty town and are going to die a protracted AIDS related death. One of the locals there told me "you know, you could move into one of the townships [shanty towns] and live like a king while fucking everything that moves; but you'll definitely die of AIDS in about a decade."