Rebecca Nurse seems to play the role of the Puritan voice of reason. In Act I, scene 3, she suggests that the people be calm and rely on God for the ultimate answer and solution to this problem. She is also the wise old woman as demonstrated by these words:
I have eleven children, and I am twenty-six times a grandma, and I have seen them all through their silly seasons, and when it come on them they will run the Devil bowlegged keeping up with their mischief. I think she'll wake when she tires of it.
It is interesting that Rebecca felt it necessary to give a resume before uttering her belief about the situation. Although her thought is justifiable, there are some acts that are stereotypical to children and she has certainly seen her fair share. However you judge Rebecca in terms of a role, it must relate to widsom, knowledge or logic.
John Proctor on the other hand plays the Devil's advocate. He uses sarcasm to illustrate that these children must certainly be fooling around. He also expresses his reasons for not coming to church. While his ideas may seem rebellious, his thoughts are really for the moral good. He doesn't want to go to church to hear only about hell. If he is going to go, he desires to hear about the goodness of God too. The role of a Devil's advocate is to always look at the circumstance from a different perspective, and this is indeed what Proctor does.