No defense has given offenses more trouble this season than J.J. Watt (No. 99) and the Texans, who harassed Broncos QB Peyton Manning in Week 3 to help Houston to a 3-0 record. (AP)

The NFL season is young, but it's never too soon to talk defense. Who's best? Tough call after just three weeks of play, but our view is that four teams have separated from the pack, and one is just slightly above the rest. Here's a look at the defenses that are providing the least friendly path to the end zone.

The top D in the NFL:

Houston Texans

Record: 3-0

Results: Week 1, defeated Dolphins 30-10; Week 2, defeated Jaguars 27-7; Week 3, defeated Broncos 31-25

Key defensive stats: No. 2 in NFL in team defense; No. 3 in points-allowed; No. 4 against the pass

Our take: The Texans top our list, and with good reason. They're 3-0 thanks in no small part to a defense that has been dominant in its second year under defensive coordinator Wade Phillips. Houston is ranked second in the league in total defense (255.7 yards per game) and third in scoring defense (14 points per game). The Texans have allowed opponents to convert just 22 percent of their third downs, which is tops in the league and contributes to the team’s league-leading 36:34 average time of possession.

The Texans are also No. 1 in the league in defense-adjusted value over average (-34.3 percent), which Football Outsiders developed to take into account numerous factors, including the opponent. Houston held Miami to 275 total yards, and the Dolphins are No. 12 in total offense (369.3 yards per game).

Peyton Manning and the Broncos had 375 yards last week, but a good chunk came when Houston held a 20-point lead in the fourth quarter. Houston has playmakers in every defensive unit. In just his second year, DE J.J. Watt is one of the best defensive linemen in football, and he currently ranks second in the NFL with 5.5 sacks. The linebacking unit is full of young impact players in Brian Cushing, Connor Barwin and Brooks Reed, all of whom have been in the league less than five years. The secondary is anchored by CB Johnathan Joseph, who made the Pro Bowl last year.

With Phillips making the calls, there are no weaknesses.

Runner-up No. 1:

San Francisco 49ers

Record: 2-1

Results: Week 1, defeated Packers 30-22; Week 2, defeated Lions 27-19; Week 3, lost to Vikings 24-13

Key defensive stats: No. 11 in NFL in team defense; No. 8 against the run

Our take: Based on the fact that 10 starters return from a unit that ranked second in the NFL in scoring defense and fourth in total defense a year ago, there are several reasons to believe the 49ers are one of the top defenses in the NFL. In theory, the new addition to the starting lineup, OLB Aldon Smith, should be an upgrade over Parys Haralson. Smith, who was previously used strictly as a pass rusher, recorded a franchise rookie-record 14 sacks last year and has since been converted into an every-down player.

The team should also benefit from its first full offseason under defensive coordinator Vic Fangio, who did not have time to install his complete defense last year due to the lockout. Linebackers Patrick Willis and NaVorro Bowman are arguably the NFL’s two best at their position and DL Justin Smith was named All-Pro at both defensive tackle and end. S Dashon Goldson and CB Carlos Rogers are coming off Pro-Bowl appearances, but there are many who believe Donte Whitner is the team’s best safety and Tarell Brown is the team’s top corner.

Through three weeks, the 49ers rank 11th in total defense, but remember this: they played against and defeated two of the NFL’s most prolific quarterbacks, Aaron Rodgers and Matthew Stafford. The 49ers are ranked eighth in run defense, and they haven’t allowed a running back to go for 100 yards in 22 straight games.

Runner-up No. 2:

Seattle Seahawks

Record: 2-1

Results: Week 1, lost to Cardinals 20-16; Week 2, defeated Cowboys 27-7; Week 3, defeated Packers 14-12

Key defensive stats: No. 1 in NFL in points-allowed; No. 2 in rushing defense; No. 4 in total defense

Our take: If the Seahawks proved one thing in Monday night's win over Green Bay, it's not that they're really good at catching Hail Marys; it's that their defense is tough as nails. The Seahawks sacked Packers QB Aaron Rodgers eight times in the game, which is five more sacks than the 49ers had in their Week 1 win over Green Bay. Seattle also held Rodgers without a touchdown pass, the first time that's happened to the Green Bay QB in a regular-season game since a December 2010 loss to the Lions.

The Seahawks defense has done more than shut down Rodgers this year, though. Through three weeks, the run defense has been stout, only surrendering 58.7 ypg, which ranks second in the NFL behind the Tampa Bay Bucs. Forget trying to score on the Seahawks, either. The team has only surrendered 39 points this season, the fewest in the league. The defense has been making opposing team's earn their points by not being susceptible to big plays. The Seahawks have only given up one pass play over 27 yards and only one run over 17 yards.

Overall, the Seahawks are fourth in the league in defense going up against three teams that have combined to go 6-3 this season. The Cardinals (5-4), 49ers (4-5) and Texans (3-6) have all played slightly easier schedules so far.

Runner-up No. 3:

Arizona Cardinals

Record: 3-0

Results: Week 1, defeated Seahawks 20-16; Week 2, defeated Patriots 20-18; Week 3, defeated Eagles 27-6

Key defensive stats: No. 2 in NFL in points-allowed; No. 2 in total sacks (67)

Our take: The sun may beat down unmercifully on the Arizona Cardinals, but the public glare sure doesn't. So how good can a defense be if no one knows about it? Turns out, pretty good. The Cardinals may not be the glamorous bunch of this lot, with only a few players who could even be considered household names in their own homes, but they sure are relentless.

The stats don't lie: Arizona ranks second in points allowed, second in sacks, first in fumble recoveries and second in forced fumbles.

Sure, their numbers were fortified by a date with Michael "Oopsie" Vick, but the Cardinals also shut down the Patriots and flustered Seahawks QB Russell Wilson on their way to a 3-0 start.

Arizona is stout up front with Calais Campbell and Darnell Dockett, linebacker Daryl Washington (three sacks) is playing as well as any linebacker in the league, and veteran safeties Adrian Wilson and Kerry Rhodes are balanced out by young star cornerback Patrick Peterson.

You may not know their names, but these guys are for real.

RapidReports correspondents Kyle Bonagura, John Breech and Jon Gold contributed to this report.

Follow Texans blogger Sean Bielawski on Twitter @CBSTexans; follow 49ers reporter Kyle Bonagura on Twitter @CBS49ers and @KyleBonagura; for more up-to-the-minute news and analysis from Seahawks blogger John Breech follow @CBSSeahawks and @JohnBreech. Stay dialed into the Arizona Cardinals with updates from's Jon Gold @CBSCardinals.