I can suggest one way of approaching an essay in which you contrast two people. It can be very illuminating too. That is to visualize any two people you know and ask yourself which one you like better. Make your essay entirely subjective based on your own likes and dislikes. That way you will be finding out things about yourself as well as about other people. What you will be finding out about yourself will be your values. If you like A better than B because A is more intelligent, then you value intelligence. If you like A better than B because B is stingy and selfish, then you value generosity.
I like B better than R because B is easier to talk to, somewhat more open to new ideas. Obviously I value open-mindedness and ability to listen. I like B better than R because B has a much better sense of humor. I like people with a sense of humor.
Or you might list the things you like about A and the things you dislike. Then list the things you like about B and the things you dislike. Your conclusion could be more about your own likes and dislikes than about either A or B.
I hope this is helpful, and I hope other people will contribute to this very interesting topic.