FF9. he only thing that I honestly disliked about FF9's world was Esto Gaza. I just really didn't like the fact that the only "winter town" in the game was concealed inside a mountain.

My second favorite would have to be FF6, specifically the World of Balance. It felt so much larger than any other world in the series (except for FF9) and it had some of the most original ideas implemented into it's design. Like Figaro Castles' subterranean transport capabilities, or the Serpent Trench. Just really cool, overall.