Hmm its hard to choose Luna, Hermione, Weasley twins, Neville, Dumbledore and Cedric are all high on my list though. But so is Tonks, Sirius and Lupin as well so I can't pick one. Honestly I like Harry too.
Luna Lovegood. she's so weird which i absolutely love. she's unique, and the way her mind works. she's her own original person. she doesn't give a care in the world (in a good way) and lives her life. there's so many things. she's someone that would definitely be my best friend.
Sirius Black. He sacrificed himself to save Harry, and was a true friend to the end. Even after Remus Lupin transformed, he didn't leave him behind. He stayed and tried to talk him out of it. If that's not a real friend, I don't know what is.
Hermione; because Harry would have never made it without Hermione. She was as vital to those books as Sam was to Frodo in LotR. She was brave, and smart, and dedicated. She wasn't ashamed of being a brainiac or demonstrating her knowledge. When hit with discrimination, she punched back ten-fold.
Also, Luna, because even though she was quirky and odd, she was extraordinarily competent and serious. She was loving and caring, curious, brave, and unashamed of herself or her father.