Bulbasaur was a great starter. Vine Whip crushed Brock and Misty. I think. It's been a while. Did Misty's Starmie have Psychic?
Charmander would put you at a disadvantage for both Brock and Misty.
Though I guess you could catch other wilds for Misty, I seem to recall that Bulbasaur was really the only thing that could really do heavy damage to Brock's Pokemon at that stage.