I have two favorites.
Hermione Granger. I mean come on, how can you not love her? Aside from being book-smart and intelligent and such a loyal friend, I consider her to be the voice of reason of the whole series. Despite all the negativity and prejudice the Wizarding World has concerning Muggle-borns, Hermione has proven time and again that she is an exceptionally talented witch, she's also very passionate about her beliefs and wanting to make a change even if it's against all odds, and that's such an admirable quality. She's just a strong female character, and what's not to love about that?
My second favorite is definitely Luna Lovegood. I love her unconventional quirkiness, her carefree spirit and how she doesn't care what others think of her, that she basically lives in her own world, but at the same time she is very brave and courageous and proves this on several occasions, I also love the friendship she forms with Harry. Plus, I think she's very relatable since everyone has a bit of Luna inside of them, aka quirkiness to our personalities, so I identified with Luna on that level somewhat.
Rest of the 30 Days of Harry Potter Challenge.