Banquo is very much like Macbeth. Having also received a prophecy from the witches, but not acted upon it, he does not give into the temptation of evil. Banquo is a brave, courageous, honest individual who is betrayed by Macbeth.
Macduff is a loyal subject of King Duncan who becomes Macbeth's worst nightmare. Macduff is also a victim of Macbeth's treachery, he survives, but his family dies on Macbeth's orders.
Like Banquo, he is the subject of the witches prophecy. Banquo is part of the first prediction, Macduff is part of the second prophecy that the witches give to Macbeth.
Macduff eventually becomes the instrument of Macbeth's undoing. Just as Banquo helps to push Macbeth further into madness even after he is dead by haunting him and causing him to exhibit unstable behaviors in front of his court, Macduff finishes the job and stops Macbeth's reign of terror.
Macbeth is a man with great ambition. We see immediately by the reports of battle in Act 1, that he is a brave man who is determined to win. We also see immediately after the witches' prophecies that he is ambitious. As soon as he hears that he has indeed been made Thane of Cawdor, thus making the first prediction true, that he considers what it would take for him to become king. We also see though, when he talks with Lady Macbeth later in this act, that he does hace a conscience because he decides that he can wait and let fate create the opportunity for him rather than for him to make it happen. As the play continues, we see him become paranoid and doubt even his close friend Banquo to the extent that he has Banquo killed and then he has Macduff's family killed because he can't get to Macduff himself. This also shows us that he is no longer troubled by his conscience. We then see him become desperate enough to return to the witches for more prophecies and then become over-confident and feel invulnerable. Finally, at the end, he seems remorseful when he tells Macduff he doesn't want to fight because he's killed too many of that family. Banquo is less complex - he scorns the witches' prophecies for the tricks that they are, he is suspicious of Macbeth (Act 2), and he wants to remain loyal to Duncan (Act 2, sc. 1).