Both Odysseus and Polyphemus are, in a way, selfish and reckless characters. Whereas Polyphemus is a one-eyed man-eating beast, Odysseus doesn't hesitate to sacrifice the lives of other people when it suits his interests. Also, Odysseus presents himself to Polyphemus as "Nobody", which is a symbolic act of dehumanizing himself, bringing himself in line with the Cyclope.
As for contrast, it is more obvious. Odysseus represents the power of human intelligence and ingenuity, while Polyphemus is almost a caricature, a grotesque one-eyed being whose only advantage is the enormous strength and the fact that his father is Poseidon.
