In terms of anime, I've definitely enjoyed Ash's run through Hoenn. When Advanced Generation series was still still active, I remember things to be quite intriguing in general, and would watch almost each and every single episode that they would air on Kids' WB (a cartoon sub-channel in US, which no longer exists). Events that were occurring here were all fun and enjoyable, and was very fond of characters that had made appearance, such as May, Max, and Drew.
As far as games go, it's the same answer--Hoenn, haha. In-game, all locations that had been put into it were all unique and different in their own way, and every time you'd visit one, it'd make you feel as if you were in an entirely different region, if that makes sense. Alongside, story-line that Hoenn had housed was very interesting, in my opinion, and Pokémon we were able to find here were special in their own right.
Aside from Hoenn, I'm also a fan of Johto, due to similar reasons, as well as Kalos.