Harry Potter, definitely.

I don't hate Twilight, but I'm not exactly a fan, either. I've read it, and while I can't say I completely disliked it, I don't really see why it's gotten so popular.

On the other hand, I've been a fan of Harry Potter since elementary school, and I can reread the series numerous times without it getting boring or repetitive to me. With Harry Potter, I actually grew to care for the characters, and many parts of the series were really thought-provoking and meaningful to me. This is a bit embarrassing to admit, but I've actually cried over certain chapters of HP before.

And I think there are a lot more meaningful themes and ideas in the Harry Potter series. To quote an icon that I've seen around on the Internet,