It's really tough for me to choose, but if I had to pick, here are three:
HONORABLE MENTION: Munich, Germany
Holy shit the food. The fucking food. Everybody thinks beer when they think Germany. I'm spoiled by beer living in Wisconsin, perhaps the beer capital of the USA. It's the food here that is incredible. Plus, you can't go wrong with the historical sites!
3. Boston, Massachusetts, USA
I never expected to enjoy Boston as much as I did, but when I went there a few years ago I had an absolute blast. Extremely walkable city with a whole lot of food, some good beer and some really awesome historical sites. Had a great time there.
2. Florence, Italy
Fucking beautiful city with incredible food, a ton of history and some amazing art museums. Also, Italian women are absolutely gorgeous. I'd love go to back here someday.
1. Prague, Czech Republic
Everything is SO FUCKING CHEAP here. But besides that, it's a beautiful city with a ton to do, from historical sightseeing (castles and shit!) to amazing food to awesome nightlife. Did I mention it's cheap? Highly recommended.