BCS model was the best model until playoffs. However 2003, 2004, and 2011 are all examples of why the BCS model was not working.
2003: USC, Oklahoma, and LSU were all deserving of playing for title and USC was left out
2004: USC, Oklahoma, and Auburn were all deserving of playing for title and Auburn was left out despite being undefeated
2011: Alabama got a rematch with LSU but arguably Oklahoma State should have been in the game
The playoff system would have solved the issue with all three of those years