For me, it London, Montreal or Frankfurt. All have broad variety. In the USA, NYC is the best.

This one is almost too easy for words.  Bangkok.

Imagine a city brimming with thousands of beautiful young girls, all willing to spend as much time with you as you want.  Zones like Patpong and Nana Plaza are jampacked with go-go bars, each one full of adorable girls.  

It is so over the top, and so unlike anything you will experience in the United States or Europe, that it almost defies description.  Bangkok is your wildest erotic dreams come true.  

It is not the cheapest place in the world (though it is much, much cheaper than in America or Europe), and there are similar scenes elsewhere in Asia.  But in Bangkok it's all right there in the open: so convenient and easy.