Here ESPN calculates roster improvement and the Panthers land at the top.
NFL - Carolina Panthers top 2013's most-improved rosters - ESPN
1. Carolina Panthers, +240.3 increase
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.
Big Addition: Rookie GM Dave Gettleman didn't need long to figure out the team was weak at defensive tackle. It wasn't just about the team needing to get some space eaters, but the Panthers needed penetration in the run game and against the pass. So they drafted Star Lotulelei and Kawann Short. The results saw their defensive tackles grade swing from minus-45.2 in 2012 to plus-23.8 a year later. Lotulelei was a huge part of that with his work in the run game, finishing with a 12.9 run stop percentage that was second best of all defensive tackles.
Given how well the Hog Mollie formula worked last year I'm thinking Getts will try it again this year but on the other side of the line. That means we draft two offensive lineman in the first three rounds. I'm leaving room for a WR early in there as I also think Getts will jump at the chance to land a skill player in the passing game. Regardless of how it shakes out I think the early focus will be to help Cam Newton. They will either help him with the protection or give him another weapon in the passing game. (Hopefully more than one in this deep WR draft)