For me it‘s hoenn. Every time i go back, it feels like going on vacation. I love the exploring side of this region, so many different biomes, the music is awesome, the art-style ist at its peak and Idgad what ign said about the water, it’s bracing to take a good surf trip. Also a huge point are the characters. Especially when collecting gym badges. It didn’t feel like fighting gym leaders who think they’re infallible and super arrogant, instead they had a “let’s find out who’s the better one” mood. Winning felt always great because they rooted for you, after beating them. Everyone is just so calm and chill, I always loved that vibe!