Two characters that lend themselves to comparison and contrast are Alceste and Tartuffe. Both are alike in being extreme versions of a personality type. Alceste is an overly honest misanthrope while Tartuffe is an overly manipulative and dishonest hypocrite. Alceste is self-destructively wedded to telling the brutal truth, while Tartuffe is self-destructively wedded to lies and deception.
As for contrasts, the two are almost exact moral opposites. Alceste is a good person who takes honesty out to fault and expects too much in the way of virtue from other people. His moral standards are too high. He refuses to realize that social interactions are to some extent made possible by compassionate fibs that take the feelings of others into account. Tartuffe, on the other hand, is evil. There is no low that is too low for him to sink to in order to get what he wants, no lie too big for him to refrain from telling. He will pretend to be wedded to chastity, then try to seduce Orgon's wife. He will pretend to be all friendship to Orgon and then try to defraud him of his home.
These two lead characters are alike precisely because in both plays Moliere is exaggerating and exposing a social vice. They are different because one represents a vice that arises from too much virtue and the other a vice that derives from evil.
Two other characters that might be compared and contrasted are Philinte and Dorine. Both characters are alike in trying to speak commonsense truths to characters who are being misled. They differ in that Dorine is lower on the social scale than the people she is trying to help, while Philinte is Alceste's friend and equal. Both plays need such sensible characters to act as a foil to the madness going on. In Tartuffe, however, Dorine might have too much influence were she higher class, while comedy arises from her situation of being the "lower" character and yet wiser than her employers.