The Buffalo Bills, Dallas Cowboys and San Diego Chargers will each be hoping that a revamped defense can get them back to the Postseason. They have all invested heavily in fixing lackluster units. Which of the three has done the best job of ensuring significant defensive improvement in 2012?

Buffalo Bills

The AFC East cellar dwellers created a lot of headlines when they signed marquee defensive end Mario Williams in free agency. Williams finally gives the Bills the kind of stud pass rusher other teams will fear and gameplan specifically to stop.

It was smart to add Mark Anderson at the other defensive end spot. Anderson notched 10 sacks with the New England Patriots in 2011 and will certainly benefit from the attention paid to Williams.

However, it will be defensive tackle pairing Marcell Dareus and Kyle Williams, who will determine the success of the Bills' schemes. The hulking duo can apply consistent pressure on the pocket and prevent guards from double-teaming Buffalo's edge rushers.

Star free agents aside, perhaps the most significant addition to the Bills' defense is the appointment of Dave Wannstedt to coordinator. Wannstedt runs an attack-minded 4-3 scheme and he will take full advantage of the talent assembled this offseason.

Dallas Cowboys

The Dallas Cowboys offseason defensive priority was to improve the secondary and they have certainly done all they can. Nabbing former Kansas City Chiefs ball hawk Brandon Carr was a free agency coup. However, the key move was the trade to draft ex-LSU standout Morris Claiborne.

Carr and Claiborne give the Cowboys a pair of corners adept in press and bump and run coverage. That's great news for coordinator Rob Ryan, who can trust the duo in single coverage, while he unleasehes blitz after blitz.

Ryan still has the league's best pass rusher in Demarcus Ware and Jay Ratliff will continue to cause problems up front. Opponents and pundits will also become more familiar with Sean Lee this season.

The inside linebacker is a budding star and his natural playmakig skills and intelligence are key to making Ryan's multiple concepts work.

San Diego Chargers

Head coach Norv Turner will be hoping top draft pick Melvin Ingram can bolster the San Diego Chargers' pass rush. Ingram is a hybrid rush linebacker who can add more big play potential to the Chargers' defense.

Adding Ingram alongside Antwan Barnes and Shaun Phillips, gives San Diego a trio of pass rushers, capable of terrorising any quarterback. Second-round pick Kendall Reyes will also be expected to make a big impact.

The powerful defensive tackle is capable of playing multiple line techniques and can be the interior rusher the Chargers' 1-gap 3-4 needs.

Which defense look strongest heading into 2012?

The Bills' new-look unit has top-10 potential. With Wannstedt calling the plays they should realise that potential.

The front four can be dominant and a secondary led by free safety Jairus Byrd, should take full advantange of the pressure up front. If Wannstedt's unit can match the exploits of offensive trio Fred Jackson, Ryan Fitzpatrick and Steve Johnson, the Bills will be strong playoff contenders.