One of the best benefits of a time machine is its healing powers, so we'll assume everyone from these teams is 100% healthy.
I think the 2012 team has the best offense in the bracket and uses some big receptions from Cooper and White to take an early lead. But McElroy, Julio, Peek, and Hanks are ultimately too much and 2009 advances late to win 23-14, behind a dominant 4th qtr D lead by Ro and Hightower. Watching Julio and Cooper on the same field is magical.
Maybe because I'm getting old I still believe the 1992 defense is the best Tide D of modern times. Not only would they shut down offenses, but they gobbled up turnovers and forced sacks. AJ uses the rollout with some success and Smelley catches several passes, but Curry and Copeland spend a lot of time in the backfield and force a bad throw that Teague high steps to a TD. The 2011 D, a dominant D in its own right, smothers Lassic and Barkley, but the Deuce contributes a long punt return and 1992 advances with a 14-9 win.
Stallings versus Saban, Mal versus McElwain, Cody and Curry and Copeland, Julio versus Langham. The first half is scoreless as each mini drive is ultimately beaten back by legendary defenders. A crossing pattern To Julio breaks big, and Ingram carries it in. Barker and company stubbornly pound away, but Cody and Ro shut down the run game and a desperation throw is picked by Barron to seal the win for 2009, 7-0.