The eponymous character of Macbeth by William Shakespeare is an unsatisfactory king in many ways. First, he intentionally murdered Duncan in order to satisfy his own lust for power. Next, he is ambitious and greedy and has little sense of kingship as a duty and responsibility; he only seems to care for his own power rather than the well-being of his country.
Oedipus also achieves power through the murder of his father, but that murder was an accident, not deliberate. Oedipus strives to improve the lot of the people of Thebes, and spares no effort to avert the pollution. His downfall is caused by a curse; even if he is an imperfect character, he is not evil, but a victim of circumstance.
Thus Oedipus is the better king.
Macbeth wants to be king just to take power. He seems to do absolutely nothing kingly once he is there. A true king is a leader and cares about his country and his people. Macbeth clearly does not. He is more interested in himself. After becoming king, he kills many of his subjects to ensure that he stays king. He also leads them into pointless battle and risks their lives to maintain his tenuous throne.
When a servant tries to tell Macbeth that soldiers are coming, he does not want to hear it and threatens the servant, calling him a coward.
Go prick thy face and over-red thy fear,
Thou lily-liver'd boy. What soldiers, patch?
Death of thy soul! (Act 5, Scene 3, p. 80)
A true king would have taken stock in the situation and actually tried to protect his men.
Oedipus, on the other hand, is at least interested in helping his people. He tries to find out what is causing the plague, and once he knows he tries to act on it.
O Tiresias, who grasp all things,(315)
even if you cannot see, you still understand
what sickness plagues our city, and we find, lord,
you alone are our savior and defender.(p. 12)
Oedipus also cares about his family, and in the end he weeps for them. So while Oedipus does make mistakes, he seems to have a heart. Macbeth does not ever do anything to benefit anyone but himself. He is in the end the more selfish.
Interesting question. At first glance, Oedipus may be considered the better king. However, his hubris makes him so blind that he becomes quite cocky and insulting to those who try in vain to help him see the truth (such as Tiresias). This is surely not a good quality in a king.
Macbeth is arguably not blind to much . . . he is fully aware of his evil acts and even their consequences, but commits them anyway.
Oedipus may be the better king since he may be found to be less evil than Macbeth surely, but he still has his major faults which should not be ignored. Really he is just the better of two evils.