Michael Carrick.
Most people started to recognize his importance and talent in 12/13 season, but before that he was completely oustanding.
His ability to play the ball forward quickly, is the best i have seen in a center midfielder. I always noticed that Fergie could take off Scholes, Anderson, or any other midfielder during a game, but he never took off Carrick, because he gave the team defensive stabality but also offered creativity with his passing. Bar that period of bad form around 10/11, id say he was our most important player since 2006, until Fergie retired.