It's not the one you think
In the run up to this weekend's matchup, most of the talk has focused on All-Universe running back Leonard Fournette going up against Alabama's impenetrable front seven. It is the most high profile matchup within the most high profile of games, so it makes sense. We want to talk about LSU's greatness going up against Alabama's greatness.
Power versus power. Strength against strength.
It's tempted to say that this matchup will decide the game, just as Georgia's inability to run with their star running back decided their matchup against Alabama.