Fictional world? The world of Discworld, of course! I'd pick Ankh Morpork for the city :)
*update* I realized from comments below that some haven't read Terry Pratchett's fascinating Discworld books yet. So: Ankh Morpork is a city-State, with an Unseen University, a brave, multi-specied City Watch and fantastic, nosy residents.
Please leave a comment in Bryan's guest post below, he is giving away lots of swag and $50 Amazon gift cards!