The best gym battles were the hardest battles aka FireRed/LeafGreen. Even Hoenn battles were difficult too aka the Twins and Wallace/Steven for champions. Also norman..... his slacking was absurd. Sinnoh was probably my favorite for gym battles, as they were both challenging enough to not make it easy, but fun enough to make me replay the entire game. After that, besides Ghetsis and N in Pokemon Black and White/2 all other gym battles were boring.... thats probably why I stick to playing the hacked versions of games. Probably my favorite so far has to be Pokemon Reborn. Its a very hard but fun game with a godly soundtrack ><