Goldenrod City, hands down, for the following reasons:
- The Department Store, naturally.
- The Team Rocket takeover side story.
- Whitney (concerning the anime only).
- Addictive mini-games. (Card flipping > roulette > slots.)
- The Underground in general, including the place where you can actually buy things to sell for later (e.g. Star Pieces).
- The girl who can tell you how happy your Pokemon are.
- THE THEME MUSIC.
- Bill. And the fact that his little sister gives you his phone number. ♥