In no specific order, it would have to be one of the following.
Azalea Town: i prefer the calm rather than the busy, hustling cities i.e Goldenrod.
You have the forest round the corner, Slowpoke Well and i really like Heracross and they're mainly found in the trees there.
Ecruteak City: Why? I'm an adventurer, i love mystery and buildings that need to be explored like the Tin Tower etc. Plus all the buildings are different than the majority in the game.
Blackthorn City: Because everybody loves dragons, right?