I agree that John Proctor and Rebecca Nurse are both strong characters, but let's not forget Elizabeth Proctor. I see her as one of the strongest characters in the play. Even after John's infidelity, Elizabeth is still willing to serve him as a good Puritan wife. Instead of ignoring that John is a lecher, Elizabeth is very vocal in urging John to go the court and expose Abigail. She does not cower to John when he defends his position about his hesitation in exposing Abigail; rather, she tells him accurately tells him that "there is a promise made in any bed." She doesn't let John off the hook when he refuses to believe that Abigail wants her dead.
Also, Elizabeth shows great strength at the end of the play when she is asked to plead with John to confess. It would be easy for Elizabeth to convince John to give the lie and save his life because of her love for him and her pregnancy. Instead, Elizabeth doesn't lead John to his decision; she allows him to make his own decision, thus allowing him to find his "goodness." This takes a very strong woman to not think of herself knowing that her husband would soon be put to death. In addition, Elizabeth takes John's infidelity upon her shoulders. She tells John that "it takes a cold wife to prompt lechery." Being willing to take blame for John's adultery reinforces why I believe she one of the strongest characters. Although some may find her weak because of these reasons, I don't. It takes a strong woman to go through the experiences that Elizabeth has and still find such love for husband.
I would choose John Proctor and Giles Corey. John Proctor because by the end of the play, he has transformed into a man of strength and honor. He chooses death rather than a lie, he upholds his wife, he refuses to give into the judges, and he doesn't care what people think.
Giles Corey is respectable because of his intelligence and because of the way he dies. Once he is convicted, he knows if he pleads one way or the other then his family will lose their land. So, for the sake of his children, Giles remains quiet while they press him to death. His only words are "More weight". He gives up himself for his family. It is almost like he is making payment for the accusations he unknowingly made against his wife earlier.
I would definitely say John Proctor and Rebecca Nurse. John of course makes an incredible transformation in the play. At the beginning he's recently come out of an adulterous affair with Abigail. He's obviously embarrassed that he did it and doesn't want to talk about it. He gets angry with his wife every time she brings it up. After his wife was arrested, the transformation begins. He knows he has to confess his sin to the judges in order to save his wife. He confesses to his lechery to try to save Elizabeth. His refusal to confess is the final stage of his transformation. At first he decides to sign his name to save his life, but he knows that it's wrong and that the Proctor name will be tarnished forever. He tears up the confession. Elizabeth sums up his transformation with line about John having his "goodness now."
Rebecca is admirable because she is never tempted to sign. She stands firm the entire time. Throughout the play, she refuses to be intimidated by the other characters. When Parris first says that Hale will be coming, she says she thinks he ought not come. She lets her opinion be know several other times as well.