My "Top" list:
1. Johto. Maybe it was just the theme song for the TV show...But Johto really did have cool Pokemon, ya'know, the ones that added on to the Kanto pokemon. But overall, I love it because of the cities and the terrain.
2. Hoenn. This region was pretty cool, what, with the contests and not, but it did lack in the gym leader category...But I was VERY impressed by the cities and the sea. The ocean seemed to have alot of effort put into it, and I love Sootopolis City. (Did I spell that right?)
3. Kanto. Who couldn't love the region were Pokemon all started out? But the gym leaders weren't that impressive and Cinnabar Island was my favorite island out of all the islands in the game. But the citie's were not that great...
4. Sinnoh. There wasn't that much effort put into alot of cities...