Hoenn all the way.
It has a desert, a forest, a volcano, several caves that are unique including an icy one and meteor falls, a route covered in falling ash, a graveyard built into a mountain, a crashed ship for the urbex lover in me, a city built in trees, a town built on logs and rafts floating at sea, a city built inside an underwater volcano, water as far as the eye can sea (see what I did there), and a marine and art museum. The music is amazing too
It was like Hoenn was designed off of everything I love.