Candice. She has an adorable design, and personality, which I think is great. She's a very strong female character, like all of the Sinnoh females, and she is a helpful gym leader who seems to have a lot of character to her.
Also, her ambiguous relationship with Maylene is the closest thing that Pokemon has gotten to a canonized LGBT relationship, two-sided or at the very least from Maylene's side, one-sided crush (besides Shauna on Serena). Which makes me very excited to see the diversity that Pokemon can bring.
Although Byron is incredibly attractive....