Well, personally speaking, I think the Gym Leaders are poorly represented in the anime. But I remember the battle with Claire being epic, because Ash used Charizard during that battle.
I remember the battle with Brawly fairly well, too....I think my top 10 would have to be...
2. Gardenia (second time)
3. Brawly (Second time)
4. Sabrina (second time, with Haunter)
Back to give competitive battling another go, then heading to Johto in March!!