To start, Macbeth is a true hero, distinguishing himself on the battlefield to protect King and country. He is truly courageous, brave and is rewarded by the king for his efforts. He does not sustain his hero status for very long, in fact, he becomes a villain, a murderer very shortly after this event.
Murdering the king makes Macbeth a villain, he becomes truly evil, consumed with ambition and desire to protect his position once he is crowned king. As king, Macbeth is still a villain, a tyrant who threatens the survival of Scotland, even nature rejects Macbeth as king.
Macduff emerges as a hero, a defender of Scotland, who is responsible for slaying the dragon, King Macbeth. Macduff makes a great sacrifice to save Scotland. He leaves his family unguarded as he journeys to England to meet with Malcolm and the King of England. While he is away his entire family, his household is murdered.
Macduff rises above his grief, his pain, his deep sorrow at losing his entire family to Macbeth's killers. He is inspired to pursue the dreaded Macbeth for revenge and to restore order in Scotland.
Banquo is not a villian, not really a hero either, more of a victim. He is murdered to soothe Macbeth's rising paranoia. He was Macbeth's friend, who shared his experience of the witches prophecy, but does not survive very long after his friend is crowned king.
He is killed by Macbeth's thugs in order to prevent him from being father to kings as the prophecy stated. However, his son Fleance escapes, and survives. In this regard, saving Fleance, he is definitely a hero, but otherwise, Banquo distinguishes himself by diaplying a sense of morality regarding the prophecies, never acting on them, something that Macbeth lacks.
The three men are different in how they allow their ambition to lead them. Macduff is honest, noble and passionate about correcting what is wrong with Scotland. Banquo is also honest and moral, never acting on the prophecy he was given. Macbeth starts out as having similar qualities to both Banquo and Macduff, but turns away from good, inspired by evil and becomes a villain.