Well....because my pokémon anime-watching started with seeing the endings of some Johto episodes, then Pokémon 4Ever, you'd think my favourite would be Misty, right?
Na....she never did enough to be likeable....Brock outshined her slightly, and he's never been a major part (particularly in DP, where he's been changed down to a combination of cooking, saying "It's Team Rocket!", "Hi, I'm Brock and I want to be a pokémon breeder!" and getting poison jabbed by Croagunk), which says something.
Dawn's voice is the most annoying yet, Jessie would be worse, but her voice is deeper xD. The fact that she "cheers" Ash on with Buneary and Piplup is also really annoying.....at least May evolved her pokémon.
To me, the fact that May was more of a main protagonist than the other two (she had her own supporting character, Max) swings it, and she also has a Blaziken and Glaceon, which are both awesome. Oh, and a Venusaur and Wartortle :D