Carolina with a + 240.3 increase from the previous season.
Kansas City comes in second with a +203.3 increase.
The article is ESPNInsider so I will only post a snippet. However, the article singles out Star, Kawaan, Luke and TD but doesn't mention a single offensive player.
Stepping Up: We'll get to why they were so much more effective, but there's no denying that the duo of Luke Kuechly and Thomas Davis delivered in 2013 with their combined grade shooting up by 12.0 points. Most of the hype has been directed at Kuechly, the tackling machine who was cast as the figurehead of the Panthers' resurgence. But it's actually Davis who graded better, chiefly because of his work in coverage. In an increasingly pass-happy league teams need their linebackers to be able to cover, and Davis is really something special in that regard. He earned the highest grade of all 4-3 outside linebackers in that facet of play.