Among the regions, which do you think was the most fun to explore? (image for illustrative purposes only)

I'm referring more to level design than anything else. Of course, aesthetics are also important—after all, if all the places look the same, it's easier to remember them—but the exploration factor (at least for me) ends up being more important. The feeling of getting an item to explore instead of just going straight through, or catching a hard-to-find Pokémon that only appears in a specific place is quite satisfying.