For those who think that the list is so obviously wrong, I'd be interested to see the list that you'd approve - top ten would be fine.
My top ten are cities which are each somewhat unique and ripe with interesting nightlife, architecture, and culture.
1.

Hong Kong - No place on earth matches the vibrancy of HK. Its still a great trip even though its being slowly devoured by the chinese.
2.

New York - Hong Kong and NY are actually tied for number 1 for similar reasons. HK edges out NYC because I find the vertical orientation of Hong Kong island endlessly fascinating.
3.

Taipei - Alternate timeline of Chinese history with an interesting melange of Chinese, Japanese, an Portuguese culture. Simultaneously hyper advanced and provincial. National Palace museum has priceless works of Chinese culture saved from the communists.
4.

Berlin - Historic divided city with gorgeous architecture and experimental nightlife. Berghain is worth the trip alone if you want to get insane.
5.

Seoul - A perspective into what NYC could be if it got its shit together.
6.

Monaco - Baller ass city state with a fun GP.
7.

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Rome/Vatican City - No explanation required.
8.

London - Origin of the anglosphere, lots of history, decent culture and nightlife, lots of stuff to do.
9.

Tokyo - Gateway into the madness of Japanese culture. Excellent arts, sporting events, nightlife, food, museums. Solid hub for branching out into the countryside.
10.
Istanbul - Culturally significant, gorgeous architecture, great food, reasonably priced.
*11.

Singapore (Just for a few days) - City states are amazing and you may as well complete the trifecta if you're already visiting Monaco and Vatican City. KL is next door if you're bored.