Since Macbeth is too complex to be labeled as villain or hero, perhaps you might wish to call upon the preternatural world of the three witches, whose expression "Fair is foul, and foul is fair" and apply this paradox to the character of Macbeth in a title for your essay. For instance, you could entitle the essay Macbeth: The Foul Hero and Fair Villain. For, in his heroic acts such as killing Macdonaldwald were rather bloody and almost villainous as, in killing Macdonaldwald, Macbeth:
unseam'd him from the nave to the chaps,
And fix'd his head upon our battlements. (1.2.24-25)
And, in his villainous act of going to murder Duncan, Macbeth is ridden with guilt and silently addresses the king, hoping that he will not suffer,
I go, and it is done: the bell invites me.
Hear it not, Duncan, for it is a knell
That summons thee to heaven, or to hell. (2.1.70-73)
While Macbeth does continue upon his murderous path, there are pangs of conscience which trouble him; he feels remorse that his wife, whom he has loved greatly has died. Indeed, he is a villain, but he is one who has not lost his heart.