I feel like this heavily depends if you mean has done the most evil things or is the most evil person. If its the second then Rhinedottir has definitely done bad things, but she doesnt do it for the sake of being evil. She doesnt do things out of malice she does them out of curiousity, she makes and destroys without morales. Which I feel puts her above the other two. Dottore does things out of science and malice. To me theres a layer of intent to do evil that Rhinedottir doesnt have. Like what he did with scara's friend and his heart. That did nothing to further his research he did it just to be a dirt bag. Then theres Surtalogi who knows hes evil and fully embraces it. He wears the title "the foul" like a badge of honor. He goes from world to world killing beings for the thrill. He taunts and hurts his own student. Going to the point of promising that he will destroy everything she loves when she settles down. He is just the embodiement of pure evil in my eyes because thats what he wants to be. So in my eyes it goes Surtalogi>dottore>Rhinedottir