For me, it's a tossup.  I have 2 favorites:

1.  1969.  Alabama 33 - Ole Miss 32. 
"In one of the greatest games in college football history, Alabama out-dueled Ole Miss 33-32 at Birmingham's Legion Field and a national TV (ABC) audience. Alabama's Scott Hunter led the Crimson Tide to a thrilling one-point win over Ole Miss junior Archie Manning. Hunter completed 22 of 29 passes for 300 yards, including the game-winning 14-yard TD pass to Meridian, Miss., native George Ranager with 3:42 left in the game. Manning was less than disappointing in defeat, completing 33 of 52 passes for a then school-record 436 yards in the loss. The 33 completions, 436 passing yards and 609 yards of total offense all stood as records against the Alabama defense."

2.  1971.  Alabama 31 - Aubs 7.
"Both teams were playing for a shot at the national championship against Nebraska in the Orange Bowl. 10–0 Alabama (#4 AP) routed 9–0 Auburn (#5 AP), and newly crowned Heisman winner Pat Sullivan, 31–7.  The Italian Stallion, Johnny Musso (22) whacked the Auburn defense for 167 yards and two touchdowns. In three Iron Bowls, the halfback ran for 467 total rushing yards, leaving him only ten yards shy of the series record."

Then Johnny Rogers and Jerry Tagge sucked the wind out of me.
We appeared shocked and unprepared compared to Nebraska that day.