Rivalries in Sports - Which Rivalries are really Rivalries?

What are the best Rivalries in Sports? Which Rivalries are really rivalries, and which ones are not? Which Rivalries are the biggest Rivalries today? Does location automatically make you a rival with another team? How do College Rivalries differ from Pro Rivalries? How do familes with fans on both side of a rivalry deal with that? Do Rivalries have to be between teams? Which sports' rivalries are the best?