All around the St. Louis Rams roster you can see improvement since the 2009 season. Even at wide receiver, probably the team's weakest link, there have been gains. 

In some instances, it's obvious. The Rams made a huge investment in upgrading the quarterback position. The offensive line got a boost from the addition of Rodger Saffold and the subtraction of Alex Barron. Steven Jackson is still Steven Jackson.

On the other side of the ball, the change has been even more impressive. Save for one outing, against Detroit, Rams' opponents are finding it hard to breath much less score points. Even more astonishing is that the Rams only made a few personnel moves on defense, most notably adding veterans like DT Fred Robbins and LB Na'il Diggs. The rest of the improvement has come from the individual growth of players and a much more cohesive unit. 

Which unit has been the most improved group for the Rams from last season to this one? Which improved personnel group has had the biggest impact on the Rams 4-4 record this year?