Personally, I would say Machiavellian Iago as there is so much dramatic irony that we as the audience understand that the characters don't. You can talk about Iago's duplicity and manipulation. Even though the main character is Othello, Iago appears the most in the play and he shares his thoughts with us. The only reason Othello is perceived as hapless is because WE know that Iago is lying and it's ironic that he believes everything Iago says while we as the audience know better. You could analyse Iago's character and how his machiavellian nature LEADS to our perception of Othello as hapless.
Maybe speak to your teacher and your peers and ask for advice?
Hope I helped a tiny bit!