Nice thread, I think there is a difference between living in a city and visiting a city, it also depends on your personal circumstances, environment and experience in each place. I come from the sticks in Ireland but spent over 4 years living in Birmingham, UK followed by 18 months in Portland, Maine, US. I then returned to Ireland, living in Dublin for a year. Off on my travels again to Sydney, Australia for a year. I have also spent a month in Granada, Spain and two weeks in Barcelona. Also lived in the small city of Tournai in Belgium for a year in between.
Birmingham was the college years for me and a huge cultural shock coming from the sticks. It has changed so much since I first went there, the city centre has been totally revamped. Personally I dont think its that bad , perhaps because I have good memories from there.
Portland seems a strange place for some but I had the best 18 months of my life there, I loved it so much. I have been back many times since, sometimes I dont get why I loved it, others I totally get it.
Dublin, I hated simple as that, dull, grey, not much of interest. Perhaps influenced by bad social experiences there after being abroad for so long.
Sydney I liked a lot even if I wasnt toatally happy there, must have been the Aussies

Lots of cool places and things to see.
Granada and Barcelona I loved, both times I was studying Spanish so lots of partying as well but still both cities are fantastic.
Tournai in Belgium will have many scratching their head but I loved it there even though I couldnt speak much French, nice little Grand Place with Beffroi and the huge Cathedral dominating everything. Fantastic place for travelling in Europe or even better, getting to bike races, the cobbles of Paris-Roubaix only 10 miles away. The last stage of Circuit Franco-Belge finished 100m from my front door.
In summary, I think I prefer smaller cities like Portland, Granada or Tournai, decent size but easy to reach the countryside also with nice architecture and history.
I must have visited over 150 cities all over the world, most recently I hit Rio,
La Paz, Cusco, Asuncion, Montevideo, Salta, Buenos Aires on a two month excursion in South America Jan/Feb.
Its hard to pick one city, I could say Asuncion which was deserted when I was there, most Asian cities frizzle your brain so dont think I would want to live in any of them or indeed most African cities. Even though I have never been to Johannedburg, it sounds worse than most in the world. I didnt have a single problem in Rio or never felt unsafe even though I was very paranoid and cautious based on all the stories, I stayed in Leblon so maybe that impacted on things.
So, being more realistic and sticking with first world cities, I will go with Dublin. I am back living in the sticks in Ireland but most of my friends live in Dublin and I visit then regularly and they always want me to move there, better job opportunites, more cultured, more modern etc but I still refuse to make the jump so....Dublin it is.