>>35115276>>35115284May and Dawn both has their own flaw and merits.
May is cuter and had better character saga, development, Personality, rivals and battles.
However Dawn stood out more as Ash's equal than May. One of May's glaring flaw is that she gets sidelined during important villainous saga/movies and often treated as a damsel in distress.
However its not surprising since May was an even worst rookie than Ash and she didn't even intended to train pokemon. She wanted to use pokemon as an excuse for traveling until she saw the bond between Ash and Pikachu that started to change her perspective. Which is why she was depended on Ash as her mentor. But she started to become less dependent on Ash as she developed and even call out Ash when he made mistakes.
While Dawn was already prepared and she knew what she going to do. So she able to act as Ash's equal instead of acting like his student from the beginning. However, Dawn felt too overconfident and she was treated more like an Ash clone.
May wasn't perfect at first and had a lot of flaw but that's what made her story better considering how she changed into a better person and trainer, I guess, the only thing May currently need is a villainous saga where she will act as Ash's equal and even rescue Ash just like he rescued her in the past.