I get asked this question a lot, when discussing my old 100% travel days (so long ago! not).. my top selections are:

Bangkok for excitement and food, Sydney for the nightlife and harbour resturants, Auckland for good memories, Tokyo for some very funny cross cultural experiences, Mexico City for the people I worked with, and Buenos Aires for the beef and red wine !

The winner is BA, a city that felt the most home from home..for a world weary northern european.