It'd have to be between Misty and Sabrina. I always catch an Abra and evolve it. Starmie is part psychic so it resists my Kadabra's attacks and its Water Pulse pretty much finishes me instantly and Sabrina, well it's just a matter of Alakazam > Kadabra and the only attack I can learn to use against a Psychic type at that point are leech life, shadow ball(stupid ghost attacks using attack type and not special), bite and thief. Every other gym leader is pretty easy, Erkia grass/posion, psybeam, Koga poison, psybeam, Giovanni Nidoking and Nidoqueen, psybeam.