So many favorites.
1. Whitney - Most personality of any GB/GBC/GBA game. Without relying on advance graphic and scenery to make the personality. GF, really did well to capture her personality using mostly dialogue. At first glance, she seems sweet and "normal" but with water works, immaturity, stubbornness, and the highest difficulty of Johto leaders, she is nothing but ordinary. She gets my vote!
2. Morty - Though a subdued character, it fits with his relaxed yet edgy new-age-monk vibe. I love the understated yet memorable gym experience.
3. Clair - Before there was Cynthia, Clair was ordering her men around to make her a sandwich. It was nice to see a strong female gym leader for the first time...that wasn't a sociopath. (Shout out to my fave Kanto leader Sabrina!)
4. Jasmine - I know, I listed four out of eight as "favorites." Probably because these were the best overall group of leaders, in my opinion, perhaps tied with Unova. Jasmine is so sweet and gentle, yet uses steel types. Sort of showing she is strong and passionate in protecting/defending pokemon, despite her demure exterior. I love her!