I've always believed the number of "haters" a person has is proportionate to the number of their fans. If they weren't loved so much, no one else would know enough to care to hate (generally speaking, some artists can be hated purely on their material/image alone).
I say it's a toss-up between Gaga and Beiber. I can't go to any youtube to watch
any music video without someone dragging their name in the comments.