I can't believe no one thought of this yet. What is your favorite region, overall?
Notes:
The Sevii Islands are counted as part of Kanto.
Other includes thing like Fiore that are from other games like Pokémon Ranger.
My favorite is Johto, actually. It's a very adventurous place, in my opinion. The main character didn't look like a noob like RGBY(Not FRLG!)'s main hero did. Your rival is more than just marginally interesting. It has all kinds of continuity from Kanto (my second favorite region, tied with Hoenn): Pokémon had a very similar style, the gym leaders rounded out Kanto's 8, old characters returned, along with Team Rocket, my favorite main bad guys, Professor Elm was an interesting change from the cool and competant Oak, the Pokémon themselves were, for lack of a better word, epic, especially the starters and legendaries, (though Mew is still, and will always be, my favorite legendary.
) All that combined with the fact that I actually liked the anime (especially the imagery for the regions) back when Johto was new. (I.E.: Before they hit Season 6, the first Hoenn one, because after the theme of the series in general changed in a way I found to be inferior to the previous theme.)
So in other words: Perfect amount of new + Perfect amount of nostalgia = Epic Win.
EDIT: Added Sinnoh. Which I somehow forgot.
) Johto also added pokemon animations (crystal), DAY AND NIGHT 
D, actual days that correspond to real time, and arguably the best generation of pokemon ever to the franchise.
and 
plus the half-land and half-ocean layout of the region.
and 
, but Nintendo thought it would be smart to make a region that has one effing giant ass-mountain (haha i love hyphenating such phrases this way), and makes the players navigate through that evil area just to reach the legendary, and in Platinum, I'm just too lazy to go through there again to get dialga and palkia. >.> Also, it just seemed the smallest compared to all the other regions, and the oceans, although small, are just a carbon copy of Johto's "ocean" split in two parts.