1. Kanto. I WANNA BE, THE VERY BEST, LIKE NO ONE EVER WAS...
2. Sinnoh. Currently has the best (albeit, it lacks Misty) characters and Pokemon teams (with the exception of Brock, whose Hoenn team was better). Paul's also a better rival than Gary because Ash constantly strives to beat Paul, whereas Gary became downright out of focus sometimes.
3. Hoenn. I found it quite boring sometimes, but the teams were nice, and like Hoenn in the games, it was colorful.
4. Orange Islands. Both it and Johto are downright pitiful, and I find the Pikachu vs. Dragonite battle more probable than Charizard vs. Blastoise.
5. Johto. Nothing but filler, boring, unevolved teams, overrated as hell, no climax, and it only got good around the tailend. He also "released" all three of his original starters, and in came Cyndaquilfail, who didn't even evolve despite being a part of over half his Gym matches, if I remember correctly. His team was horrible, the battles (except the Silver Conference ones) were horrible...the entire arc was just an abomination to the anime. It was so bad, it made me quit Pokemon up until the third generation, and since the anime hadn't gotten much better by that time, I quit again. It took Sinnoh to bring me back. >_>
BTW, shouldn't this be in the anime forum? :|