The Marino vs. O'Brien rivalry was a GREAT rivalry. As a fins fan, even I have to admit some of the games those two had against each other were absolutely classic...especially the 51-45 OT shootout in 1986. O'Brien wasn't a great QB and no where near what Marino was....but he was a pretty damn good QB.
The one I hated was Fiedler vs. Testaverde. It always seemed that during these games when the Phins played the Jets....Testaverde was at his best, while Fiedler was at his worst. I'm still not over the Monday Night Miracle game.
The Favre vs. Pennington rivalry only lasted one year...however it had a sucky beginning, with a GREAT ending. :)