This is a good question. Shakespeare's Macbeth is a tragedy, and it follows the rise and fall of the title character. Macbeth's antithesis (opposite) in nearly every way is Macduff; yet, there are several points of comparison which you can effectively support.
First, they are both loyal to their king, Duncan. When we meet Macbeth, he is fighting valiantly for the cause of his king and was rewarded for it. Duncan felt safe enough to trust Macbeth as his host, as well--much to his peril. We know Macduff is a trusted nobleman because he was given the task of waking Duncan in the morning--when the king was at his most vulnerable.
Both men are passionate for a cause and willing to kill for it. Macbeth killed as a soldier and murdered as a king; Macduff was motivated by both love of country and revenge for his murdered family to kill the usurper king Macbeth.
Despite their many differences, Macbeth and Macduff do have some common characteristics.