I have answered this question a few times, and my answer is still the same. My pick would be Montreal, Canada. I think the main thing that attracts me to it most, is the vast difference in culture from the US. When you walk down the street, you almost feel as if you are not even in Canada, as it has a more European feel to it. Could be because most everyone there speaks french.
You also quickly notice that the Canadians in Montreal are even more "free spirited" than those in Toronto. Things that would make American's nervous are right in the open on display. Their clubs and bars make most American bars seem very dull and boring. It's just so different, lively, and clean.
I thought about writing a hub about Montreal, but there is so much to tell, I think my head would explode from trying to get out all the information. I have been to the city twice, and each time was a very wonderful experience. I would go back again every year, but, I can't afford to travel that much any more.