One school of thought, with which I agree, is that Caliban and Ariel both represent, in part, different aspects of Prospero's identity. It is also important to consider that Shakespeare may have aligned himself with Prospero (see the end of the play where Prospero gives up his book and staff); many think this most likely last play by Shakespeare is Shakespeare's way of saying he is retiring from writing. Keep in mind, too, that it is the good, the bad, and the ugly that make up human identity, and even those parts have their good, bad, and ugly aspects, as well. Shakespeare's works, God bless them and him, ask the audience to think deeply about human actions, thoughts, beliefs, prejudices, motivations, dreams, aspirations, victories, failures, and much more. But Caliban and Ariel play other roles that address the human interests I have just mentioned. Shakespeare, thankfully, never made it easy. :o)