Iago, most definitely...Hands down! He is a pure villain from start to finish. It is the way in which he plans and does it all and has no remorse at the end. He is pure villain and knows the consequences could be either to his advantage or not. He knows he will win but may lose his life. His actions are put into motion and he follows through without hesitation. He is so darn sure of himself he is arrogant and yet the most villainous part of him is his apparent charm and goodness, everyone referring to him as "Good Iago". If I could love a villain, it would be Iago. The reasons have all been stated so eloquently in the last 5 or more posts about him.
Yes, "Othello" is one of my favorite plays, I know it is because of Iago....He mesmerizes me with his scheming. Maybe this play should be named "Iago" and not "Othello". He is more than a plot device. He is the play!