Kanto.....at least in Johto and Orange Islands his Charizard obeyed him and he got a Snorlax......
It had some genuinely weird episodes, like with Sabrina...the only good part out of that little story arc was when they went to Pokémon Tower. It didn't even make Giovanni's gym battle good, whereas I've heard Johto had an epic dragon battle involving Dragonites and Charizards in the story arc involving Clair's gym.
I personally liked Sinnoh better as it at least made nice gym battles. But Hoenn's my favourite. Orange Islands was meh, so I include that with Kanto because there weren't any new pokémon (Well, there was the now ritual new-gen-pokémon-appearance), but it was mainly Kanto stuff that hadn't been covered by the end of the Indigo Plateau pokémon league.
So, yeah....Kanto.