Ah, Hoenn. After all the repels done, I love that map. We hopefully will have the remake after X/Y, and with all the new features (ease of using repels, faster surfs etc) I'd see it as one of the best games.
Sinnoh was my least favourite map in terms of aesthetics (not that it was bad). Johto combined with Kanto was great, and Unova was pretty cool as well.
Kalos though on first glance is amazing! Seems very non-linear as well, which can't be said about Unova, Sinnoh and Hoenn.