Most Favorite: Johto
Come one, it introduced Porygon2, a clock, and all the other cool stuff!
Least Favorite: Hoenn Sinnoh
Sure, it made it much easier to get Porygon, added tons of new features, and got rid of the annoying link cable, but in the end, it's the most bland out of the 4, it doesn't have the same sense of mystery that Johto and Hoenn had, it doesn't have the class of Kanto, and after a while, it gets bland having to do the same things over, and over, and over again. I still love it though.