May. I liked the fresh approach she brought to the show with contests. Since Dawn is doing something similar, there is a lack of this "novelty" appeal that May had as a character. And her personality is borderline between sweetheart and strong-willed. Plus, I can actually view May and Dawn as important characters rather than mere "sidekicks," always a plus when most females in anime are mere "cheerleaders" for the main bloke.
I don't know why so many people prefer Misty, but then again I'm that nutjob who thinks that Season 1 is overrated beyond belief.