Of the characters named, the ones who really only could qualify are Jaime and Cersei, who both perform 'evil' deeds which lead, or should lead, to the deaths of innocence. A lot of the others act without thought for the consequences. Theon is cruel and uncaring, but not evil as such. He spares Bran and Rickon when he had a chance to kill them, for example, and was happy to let the realm condemn him as a child-murderer.

As for Arya, she is becoming increasingly desensitized to violence and is clearly suffering from stress-related disorders, but the people she has directly murdered have been enemies of her house, people trying to kill her or a deserter from the Night's Watch. The only true innocent she might have been said to have killed was the stableboy, but he was trying to kidnap her and she did act in self-defence.

And Robert was on the list but Tywin wasn't? Or Viserys? How does that work out?

And no Littlefinger? By his own admission, he ferments chaos which results in thousands of innocent deaths purely as a game to amuse himself. By that definition, he is the most 'evil' character of them all.