I was talking with someone at work about cool stuff I've done in Cincinnati, and they asked (cynically) "do you think every city is as cool as Cincinnati?" I replied that I didn't really have a whole lot to compare to, but immediately realized that that's not really true. Cincinnati's the only city I've lived in, but I've visited a few major ones. Below are a list of the cities that come most readily to mind, roughly in the order of which I'd be most eager to return to. Some I've spent very little time in, so this is a very subjective ranking.
(every other place I've ever been)
Update: thanks Racahel, I had forgotten both Barcelona and Queretaro, both of which I enjoyed alot.