The key with defenses is finding defenses that will face a lot of passing plays. Fantasy point-scoring events like interceptions and sacks occur exclusively on passing plays, and fumbles actually occur more on passing plays than running plays. Defensive touchdowns are difficult to predict, but they're also more likely to occur on passing plays with 53 pick sixes last year compared to only 33 scoop 'n scores.
One of the best ways to identify defenses that will face a lot of passing plays is identifying Vegas favorites, preferably home favorites. And obviously the lower the opponent's implied point total, the better the matchup for the defense.
Premium Options
Minnesota is the obvoius D/ST choice this weekend. For starters, their opponent, Houston, has the lowest implied team total in Vegas this weekend (17). And then there's the fact that Minny's defense is extremely stout. The Vikes rank third in Football Outsider's defensive DVOA, and they lead all defenses in fantasy scoring by a wide margin. The only reasons not to roster Minny's defense are a) because you're playing in a GPP and need to be contrarian, or b) because you can't quite afford them in your cash lineup.
If you can't quite afford the Vikes, Los Angeles makes sense as a slightly cheaper alternative as they're cheaper than Minny across the board.. The Rams will host the Bills who have the third lowest implied total of the weekend. St. Louis' defense ranks 12th in DVOA so far, though they rank seventh in FO's DAVE rankings, which still include preseason projections to account for any small sample size issues we may still be dealing with. The Rams won't be nearly as popular as Minny, but they should still see a healthy rate of ownership, so you might get even more contrarian still in GPPs.
One other team that might be considered a premium option by some is New England. But the Pats haven't been good on D this year as they rank 26th in DVOA and 24th in the DAVE rankings. They'll also cost you as much or more than Minny's defense, so what's the point?
Sneaky Option
This category is reserved for good defenses that may be overlooked in a given week for whatever reason, providing you with the opportunity to roster a really good unit with a lower ownership rate. The team that most fits that bill this week is Baltimore. The Ravens rank fourth in both DVOA and DAVE, and they'll host Washington who has the sixth lowest implied total of the weekend. Baltimore is cheaper than all the most obvious defenses this week, and they figure to not be all that heavily owned. Give them a long look in GPP lineups.
Value Options
If you're looking to go as cheap as you can with your defense, don't look further than the Ravens on FD. But on DK Miami is worth a look. They're a home favorite playing host to the Titans who have the fourth lowest implied total of the weekend. The Titans have also allowed the second most fantasy points per game to opposing defenses, so the matchup is great. Miami ranks middle-of-the-pack in DVOA and DAVE, but the matchup is definitely good enough to overcome that.
Miami will see a decent amount of ownership, so if you want to be a bit more contrarian but still go cheap at DST, take a look at Cincinnati. The Bengals rank seventh in DVOA and ninth in DAVE, so they're a solid unit. They're only a one-point favorite on the road in Dallas, and the Cowboys have a decent implied total of 22.25. But that's why this is a contrarian option and not an obvious one. The Bengals are a good enough defense to return some value on their DK price tag.