Half of this question would be easy to answer; the other half, of course, is a little trickier to find, since we don't always expect to find a lot of positives in the midst of conflict. So, I'll concentrate on helping you think of some "bests" which show themselves through the course of this play.
The "worsts," of course, include: deaths, greed, heresy, lies, accusations, loss of faith, lust, envy, corruption, lying...and the list goes on.
The "bests" are fewer but represent the finest aspects of human nature when faced with conflict:
John and Elizabeth had a broken, awkward marriage due to John's infidelity; however, as each of them tries to save the other from the punishment of death, their love is renewed.
John is a man who has succumbed to his carnal desires and broken his faith with God and man; however, as he is forced to choose between his life and his name (his soul, that which matters), he is able to forgive himself and accept God's forgiveness.
Giles is a cantankerous, litigious man who keeps his friends and neighbors on the edge of a lawsuit; however, he is able to withstand both the figurative and literal pressures of this inquisition and save his land and holdings for his family,
The Reverend Parris was a haughty, arrogant, and self-absorbed man; however, this experience appears to have humbled him, and he now has the potential to become a true man of God.
The loss of these righteous community members (particularly Rebecca, Martha, and John) is a tragic waste; however, it is their deaths which precipitate the end of the court and the trials.
This should get you started on your essay--it would be an interesting one to write, with a clear structure built in to the prompt. Happy writing!