Flintlock
Pro Adventurer
The Highwind, because it can take me pretty much anywhere else in the game pretty quickly.
Also, I'm surprised no one's said Gold Saucer.
The Gold Saucer felt like a place where everyone was forced to have fun, rather than being allowed to find it naturally. The music got annoying very quickly and its location made it very time-consuming to race Chocobos, go back to the stable, mate them, feed them, and go back to racing them. Also, the owner's a bit of a jerk who gives people life imprisonment without a fair trial