Go deep.

Helen of Troy, known as the face that launched a thousand ships. Daughter of Zeus and the most beautiful mortal goddess. Loved by Paris. A protagonist.
Penelope, wife of Odysseus, the protagonist on the Odyssey, who had one hundred eight suitors during her husband's absence. A symbol of connubial fidelity. (http://en.wikipedia.org/wiki/Penelope)

Compare and Contrast

In my point of view, I see Helen and Penelope as two beautiful women. With Helen having the face that men cannot resist and with Penelope, having many suitors and remaining beautiful despite her age. Helen is considered as a protagonist in the movie Helen of Troy despite the fact that she became unfaithful to her husband because she went with Paris to Troy. She did a thing that a wife should not do. But what she did is often considered by the watchers of the movie as a strong move, fighting for the one you really love. And even though their love for each other (Paris and Helen) ruined Troy and the other homes of Trojans, we still see them as protagonists because they fought for love till the end.

Meanwhile, in the Odyssey, Penelope is not considered as a protagonist but her husband, Odysseus. However, she is one of the main characters. Although, she has not seen her husband in twenty years, she remained faithful to him. A love that endures and is patient.

I consider Helen as the antagonist on the poem because she was the reason why all of the chaos happened. The Trojan war, the death of Paris and Hector, and the destruction of the lives of the Trojans. On the contrary, I consider Penelope as the protagonist compared to Helen because of her faithfulness and unchanging love to his husband despite the distance and not knowing if Odysseus is still alive or not.