My favorite Harry Potter character is Harry himself. My guess is he is the most popular character, if only for the fact that he is the central character in the stories. To me, Harry has the appeal of the heroic under-dog. The reluctant champion who does not always have the answer, or know his own strength.
Harry is also an orphan, and I think everyone relates to that, at least in spirit. I know I have had times in my life when I felt like an orphan, or so I imagined, and something in the way Harry deals with his difficulties with humility and courage is very admirable and inspiring to me.
The other characters in Harry’s world are loveable as well, both friends and foes. They are wonderfully drawn by Rowling, and we learn a great deal of them through Harry’s eyes. Brilliant Hermione, steadfast Ron, fatherly Dumbledore are all part of a wonderful cast that millions have enjoyed.
The Harry Potter series is not just about wizards and magic and a fantastic hidden world, it is the story of a boy who overcomes adversity and grows into an identity that might have stayed hidden forever.
I like witches and dragons and the like as much as anybody, I guess, but it is the characters that really take hold and make a good story a lasting treasure.