Seoul. The city is so damn modern and the energy of Korea is amazing. It's so easy to get dragged into the fast-paced, high-energy lifestyle just by being exposed to other people long enough. Transportation is cheap, it's very easy to reach other places in Asia and Korean people are very friendly (IMO). If you like technology and shiny new things, Korea is definitely the place to be.
Do you know the language? Is it necessary to in order to feel that life is as fast-paced as you mention?
Koreans are also a bit racist but if you do not mind it's fine.