Instant Debate: Which defense can challenge Seahawks for supremacy?

The Seattle Seahawks have fielded the NFL's No. 1-ranked defense in each of thepast two seasons. But during the offseason, the 'Hawks lost defensive coordinator Dan Quinn (now the head coach in Atlanta) as well as key contributors like Byron Maxwell and Tony McDaniel. And the unit is still waiting for its dynamic safety duo to hit the field in game action: Earl Thomas is rehabbing from offseason shoulder surgery, while Kam Chancellor is holding out.

Now, obviously, Seattle's defense still could -- and should -- be one of the NFL's best in 2015. But it's plausible to think somebody could knock the Seahawks off their No. 1 perch in total D. Looking across the league, which team has the unit to challenge Seattle's reign of defensive terror in 2015?

The Bills have a very good chance at fielding the top defense in the NFL, especially if they tighten up some things against the run. That should be plausible, considering the lack of star power at running back on the rosters of their AFC East foes. Buffalo also will be playing an offensive scheme designed to keep the ball away from opponents -- which, in theory, will keep the D fresh. Look at what happened in Dallas last season.

Buffalo's front four is as good as it gets in the NFL. This quartet gets after the QB and, in the process, forces fumbles. That's huge. And don't forget: Veteran DE/DT Red Bryant is now in the rotation, and he's a solid player and leader. The linebackers and guys in the secondary will be very aggressive, which will leave them vulnerable, but it also puts them in position to make plays. The Bills were one of the top teams in terms of forcing turnovers last season, and that should not change.

A couple of sleeper defenses that should be in the mix for the No. 1 spot, along with the Bills and Seahawks: The Chiefs, Vikings, Browns, Broncos and Cardinals. Oh, and I do not think that the Lions' unit is just going to fall apart without Ndamukong Suh, either. I'll give you two teams with under-the-radar defenses to challenge Seattle's group: Arizona and Houston.

The Cardinals' defensive line is fantastic -- Calais Campbell never gets the respect he deserves. Patrick Peterson is fully healthy, something the game-changing, playmaking corner never was last year. And Tyrann Mathieu should be back to 100 percent, as he was during his rookie year (before he blew out his knee). The Honey Badger wrecks offenses with his nose for the football.

Houston is so well-coached and has the game's best defensive player in J.J. Watt. Jadeveon Clowney is back on the practice field, and I still believe he can reach his potential and upside. Brian Cushing is healthy, which is huge for this unit. Lastly, the defensive backfield is improved, as the Texans spent their first-round pick on cornerback Kevin Johnson. Seattle will be hard to beat out for a number of reasons, two of which have nothing to do with defense. They have a great running game with Marshawn Lynch and Russell Wilson and a stadium that is very hard for offenses to play in. That being said, I think two contenders who ranked highly last year might challenge Seattle. Denver, which ranked as the third-best overall defense in 2014 and is led by a new coordinator in Wade Phillips, will take on an aggressive approach with its front seven. The Broncos have a chance to be strong against the run and get pressure with their pass rush, which should get a boost with the addition of first-round pick Shane Ray. At corner, I like Aqib Talib and Chris Harris; if Bradley Roby improves, that will only make the team stronger at that position.

My other nominee is Buffalo (fourth-best D in 2014). The Bills have an outstanding and seasoned front four that can rush the passer and defend against the run. But how good is their secondary? Another sleeper team to look at is the St. Louis Rams, led by dynamic pass rusher Robert Quinn. I like Buffalo. New head coach Rex Ryan -- a defensive mastermind adept at conjuring up effective schemes -- and coordinator Dennis Thurman will get this group to outdo even last year's impressive performance. The 2014 Bills led the NFL with 54 sacks and posted more picks (19) than touchdown passes allowed (16), in addition to notching a turnover differential of plus-seven -- all stats that point to a pretty good unit.

Most of the key players, including those on the Mario Williams-led D-line, are back in 2015, while second-round pick Ronald Darby should add to the secondary. Finally, the defense should get a boost from both an improved offense, which should reduce the amount of time the defense is on the field by about two minutes per game, and the fact that the Bills' final two contests will be at home, likely in the kinds of conditions that favor defensive play. Look, I'm not betting against the Seahawks until I see them outplayed with my own eyes. They're still the most talented and well-prepared defense in the NFL. But for the sake of this raging debate, how about the Miami Dolphins?

Ndamukong Suh's presence alone completely changes the line's ability to push the pocket and disrupt opposing passers. To help, the game's most dominant behemoth east of 
J.J. Watt is flanked by 
Olivier Vernon and the perennially underrated 
Cameron Wake. 
Brent Grimes, meanwhile, gives you one of the AFC's top cornerbacks in a secondary that will benefit from the constant attention placed on Suh and Co. up front. 

"I don't have a problem saying this, but I think personally we have more talent than we had in the No. 1 defense last year in Detroit," Suh said this week.

I still see Seattle as the unit of choice, but no team added a bigger chip on defense than Miami. Suh will wreck game plans from wire to wire. The Bills' defense could overtake the Seahawks' unit as the NFL's top defense. Rex Ryan inherits a talented group that features the top defensive line in football. Mario Williams, Marcell Dareus, Kyle Williams and Jerry Hughes can wreak havoc on opponents on traditional rushes, but Ryan's ultra-aggressive approach will lead to more one-on-one changes, resulting in more sacks.

Considering the talent in the secondary ( Stephon Gilmore and Aaron Williams), the Bills' attacking style could produce more takeaways and W's in Ralph Wilson Stadium this season.