Magneto. I like how his character isn't plain good or bad the way the overwhelming majority of characters are portrayed. He has the capacity for love as well, he's expressed it to his kids, and he's always valued Charles and was always his friend despite the fact that they wanted different things. His past made him a bitter person who doesn't believe in peace, it made him cruel, but he's still human and is capable of deep feelings, and empathy, and, unlike many other villains, he always has a lot of class.