The Houston Texans have the best secondary in the AFC South, or at least they did in 2011.
It's difficult to separate out secondary play from defensive line play because the most important important component to any good pass defense is an elite pass rush.
As I went to rank the secondaries in the AFC South moving towards 2012, I did my best to separate out the actual play of the corners and safeties from the performance of their defensive line.
1. Houston Texans
The Texans rolled the free-agency dice last offseason and hit it big with Johnathan Joseph. His outstanding play helped the Texans post the best defensive passer rating in the NFL. The Texans did lose Jason Allen in free agency, meaning Kareem Jackson will have to play more in 2012. That isn't a good thing. The Texans also have serious questions at safety where Danieal Manning is now 30, and Glover Quin struggled mightily. Joseph is the single-best secondary player in the entire division, and if he goes down with injury, the whole Texans secondary could collapse.
The Jaguars until very recently fielded one of the worst secondaries in the NFL. Their defensive passer rating in 2011 was middle of the pack, but had been 31st in 2010. The Jaguars secondary was riddled with injuries in 2011, but had gotten good play from guys like William Middleton before losing him to the injured reserve. They bolstered the secondary with the signing of Aaron Ross. It might not be a great unit, but it's still probably the second best in the division.
The Titans had a great year in limiting yards per pass play in 2011, but losing Cortland Finnegan was a serious blow to their secondary. This unit got so little help from its pass-rushers that I would probably have ranked it first overall, but losing its best player dampens my enthusiasm for the unit as a whole. Still, the Titans have Jason McCourty, who had an excellent season in 2011 in doing a little bit of everything including leading the team in tackles, picking up a sack and intercepting two passes.
Worst. Secondary. Ever. Antoine Bethea is a very good player, and a true warrior. Jerraud Powers has talent but can never stay healthy. Everyone else is a replacement level talent at best. The Colts' biggest mistake in 2011 was not rebuilding the secondary. Terrible quarterback play did in the team, but even if Peyton Manning had been healthy, the secondary was too weak for the team to be considered a serious contender.