Alot of great places, but the "best" depends upon timing.....

At 22, my first extended stay in NYC.

At 42, a week of business in Edinburgh, sandwiched between a week of liesure, mostly, in Southwest Scotland and a week of liesure in the West and Highlands.

At 69, almost by accident, Olomouc, Czech Rep., a combination of circumstances and people which made almost an accidental visit rewarding and more than memorable.

Barcelona, 1964 and 2010, proving that Wolf was wrong. "You can go home again." (and "Why did I not return sooner?")