Aristotle defines tragedy as a story in which a character experiences a dramatic reversal of fortune, thus prompting catharsis in the audience. Catharsis is a purging of emotions—that is, subjecting the audience to scenes that inspire tears and then leave them feeling emotionally cleansed after leaving the theater. This certainly occurs in Antigone, where the titular character's desire to do good in properly burying her brother (thus honoring the laws of the gods) gets her arrested and killed.
By Aristotle's definition, both Antigone and Creon could be seen as tragic figures since both experience reversals in fortune, though as far as heroism goes, Antigone is the more heroic figure by far. She shows courage in defying the law. However, Aristotle also believed a tragic figure should be morally complex in showing both good and bad traits, and this definition fits Creon more than the noble Antigone. Creon is tyrannical, but he also believes he is doing the right thing and establishing order. It is only at the end of the play when he realizes his lack of tolerance has cost him dearly and made him turn against the gods.
Lastly, whether or not Antigone's fate would have been less harsh had she been a man is up for debate. Had Antigone been a man, she might not have been executed and her rebellion might have been taken more seriously as just civil disobedience. That Antigone is a woman who goes against a man's laws is especially significant since ancient Greek society was intensely patriarchal. She is not just breaking a law, but going against the ideal of female submissiveness to male authority.