College Football: Oklahoma vs. Texas, Oklahoma State or Nebraska (back in the days when Tom Osborne coached).
Pro Football: The Dolphins - and whoever's playing the Cowpokes!
Baseball: Yankees vs. Bosox is the only rivalry that matters. Jints vs. Bums (SF (formerly NY) Giants and LA (formerly Brooklyn) Dodgers) are irrelevant since they turned traitor and moved west over 40 years ago
Hockey: Don't follow it seriously enough to pick sides.
Basketball: Ditto, except when the San Antonio Spurs are gunning for the finals! Now that's a team with class.