Although it's up for grabs now if it's really fictional but my choice would be Shangri La !
What's your favourite fictional city?
The Lost City of Atlantis. I would love to see it in person!
Hogsmeade
Ankh-Morpork.
The completely believable and carefully constructed city at the centre of many of the Discworld books. (If you do not know what I am talking about, shame on you.)
Far Far Away
Not a city, but my favourite fictional place would have to be Xanadu.
In Xanadu did Kubla Khan
A stately pleasure-dome decree:
Where Alph, the sacred river, ran
Through caverns measureless to man
Down to a sunless sea...
Gotham
Mayberry
Tai-tastigon