Dawn in my opinion, she was smart and had a very well thought out contest style. Also unlike May, Dawn didn't just catch cute looking Pokemon. She had Mamoswine and Ambipom, they may not have been cute looking, but she showed their inner beauty in the contest. She also won her ribbons a lot faster then May, heck she also beat May in a contest. Dawn never had strong looking Pokemon, yet they were still really strong. I loved that about her, she shows the real spirit of Contest. montrer your Pokemon's beauty and how strong they can be.
Sometimes I think May's style would be better in Gym Battles. But she still has a good Contest style and she's pretty good at it.
May because May had way plus final evolutions than Dawn. Dawn hasn't evolved her piplup yet and May had Blazien,Venusaur,Wartortle, And Dawn only had Mamoswine. And Dawn even gave away her ambipom for the pingpong master. May is better than dawn I think.
If toi ask me Id say Dawn cause 1.you guys are doing it who has stronger pokemon and not who is a better coordinator.2.Dawn beat May on a contest.Well I shouldn't say but I just think Dawn is a better coordinator