A.B. had lots of exciting episodes (at least for me), but many of my favorite episodes appeared during the Sinnoh era. I really loved all the episodes with Pokemon Contest. I really loved watching Zoey and Glameow. Laughed hard, every time I saw "Jessilina" in contest.
As for the Theme song I prefer the original Japanese language versions "Rivals" "OK" "Pokemon Symphonic Medley".
Kinda a tie between Johto and Hoenn. I first started getting into the anime when Johto aired here, and Johto is pretty much my favourite regions of all anyways. There were so many episodes of those seasons that I simply love, and that's pretty much it. As for Hoenn, I think I mainly liked it because most of my experience with anything from the third generation actually comes from the anime. It's the only region other than Kanto that I've watched fully through in the anime, and it still has some of my favourite episodes.
The other ones are great too, but these are just the ones I've always loved the most :D
I've not watched Pokemon since the originals but how can anything get better than the originals? The Venustoise fusion dance... the ancient giant Jigglypuff, Gengar and Alakazam... the "Island of the Giant Pokemon" theme park... the vengeful Tentacruel... Sabrina's dollhouse... the emotional Bye Bye Butterfree... Charizard's attitudes... it was so imaginative, surreal and heartfelt back then.
I really got behind the Johto series...that comprised most of my childhood so I will always be bias towards it!!...from the cool theme songs to the cool pokemon to the cool region itself.....it could do NO WRONG..
PS...RA'S AL GHUL!!!...I would challenge you to a fight to the death!!...if only you didn't have those DAMN lazarus pits!! LOL
The seasons we watch during our childhood really make us love pokemon because it's when we believe in things the most. Personally Johto and Kanto were my favourite, because I got to see Charizard, which was just astonishing, and so I really liked it
I adored early-mid Johto and pretty much all of Hoenn. The latter brought some really great characters to the series and they had great relationships, especially May and Drew (and Harley)! Johto was mostly for nostalgia purposes haha. xD;