Antigone is the most likely candidate for protagonist of Antigone. There is actually a bit of debate about this. Creon gets way more stage time and goes through a more distinct character arc, which leads some to argue that he's the real protagonist. The best case for Creon as protagonist lies in the fact that he is the one that experiences Aristotle's concepts of peripeteia and anagnorisis. Both of these were important elements for a tragic hero or heroine to have.
The peripeteia is a reversal of fortune. Creon certainly experiences this. The tragic events of the play transform him from a pillar of pride into a puddle of humility. After his downfall he experiences anagnorisis or a recognition. He realizes the law he passed was a really bad idea and regrets his pride. Antigone on the other hand, knows exactly what is going to happen to her from the beginning of the play and never regrets a thing.
So, yes, there's a really good argument for Creon as protagonist, but check this out. Antigone is the one who drives the action of the play. She is the one who sets the tragedy into motion. She is the one who buries Polyneices despite Creon's strict edict. It is Antigone's suicide that causes her fiancé Haemon to stab himself, which in turn cause's Creon's wife Eurydice to commit suicide. Also, it certainly seems like we're supposed to be sympathizing with her toward the end of the play, not Creon. The king himself comes over to her point of view. There's room for some friendly debate here, but it seems to us that Antigone is the center of the storm.