Athena v Poseidon
I think that the rivalry between Poseidon and Athena is interesting and shows their clashing personalities. They seem to be opposed in everything that they are both involved in. First, in the history of the Parthenon we find that Poseidon and Athena fought to win over the Athenians to be the patron of Athens. While Poseidon gave them naval superiority from striking the rock and giving them sea water, Athena gave them an olive tree, an idea of prosperity and peace. Also, in Book 13 of the Odyssey we see them on opposing sides once again. Athena has helped Odysseus find his way home and continues to help him come home as a hero and defeat his wife's suitors to return to power, while Poseidon has done everything to stop his journey and hurt Odysseus and anyone who helps him. They are both very demanding personalities who are quick to punish and condemn. When on opposing sides, they will do anything to hurt the other and win whatever competition is put before them.