This is MLB's best team (it's not the Red Sox)

The Astros aren't going to win the most games in baseball this year, because the Red Sox will. Houston won't have the top seed in the American League playoffs, because Boston will. A year ago at this time, the Astros were celebrating a division title, thanks to a 15-game lead over the Angels. This year, they won't clinch the AL West for at least another week, since the A's are only four games behind, and the two were tied as recently as Aug. 21. 
All of this might imply that this year's version of the Astros aren't quite as good as last year's World Series champions. That would be incorrect. This year's team is better in some ways and worse in others, but the larger takeaway here is this: They're the best team in baseball, and no one else is better positioned headed into October. No, Houston won't win as many games as Boston will. It doesn't matter.
Let's start with that AL West race, which has been a close one all season, with the Mariners surging early and the A's surging late. In 2018, the Astros have never had a lead larger than six games, which they had for a single day on July 24. In 2017, they built a six-game lead on May 10, and it was never closer than that for the remainder of the season. If you only knew that information, you'd think Houston wasn't as strong this year.
The problem with that is it's not true, once you compare this year's Astros team through 149 games against last year's club.
2018: 94-55 -- .631 winning percentage
2017: 91-58 -- .611 winning percentage
That's better, obviously. That there's a division race says more about the quality of the Mariners and A's than it does about the Astros, because last year's AL West was especially weak -- Houston was the only team to finish with a winning record. This year, the competition is far stronger; with a solid finish from the Angels, four of the five teams could be at or above .500.

While it's true that the Astros' offense hasn't quite piled up the runs like it did last year, the club has improved its run prevention considerably, to the point that it's bordering on what would be historic run differential totals. 
2018: 741 runs, 494 allowed -- 5.0 runs/game -- 3.3 runs allowed/game
2017: 815 runs, 664 allowed -- 5.5 runs/game -- 4.5 runs allowed/game
Another way to say that is that the Astros have outscored their opponents by 247 runs, the most in baseball, a year after outscoring their opponents by "only" 196 runs, the third best in baseball. If we give them credit for their current pace through the end of the year, that would get Houston to a run differential advantage of 269 runs, which would be the largest by any team since 2001. It would be the third-largest differential in the divisional era, dating back to 1969, which comprises nearly 1,400 team seasons.

Look at those teams, won't you? The 1998 Yankees are routinely in the conversation for "best team of all time." The 2001 Mariners faltered in October, but they won 116 games. In addition to the '98 Yankees,1975 Reds, and 2016 Cubs all won the World Series. You don't get here by accident. You get there by dominating.
That's exactly what the Astros have done, really. They're the best offense in baseball by advanced metrics, in part because they have the second-lowest strikeout percentage (19.6 percent), the fifth-best OBP (.331) and the seventh-best team slugging percentage (.430). Once Tyler White takes his next trip to the plate, Houston will have nine hitters with at least 200 plate appearances and above-average performance, the second most in baseball. (That the Astros have "only" the fourth-most runs scored may be credited in part to the shockingly pitcher-friendly nature of Minute Maid Park.) 
On the pitching side, it's even more impressive. The Astros have the lowest ERA (3.12), the lowest FIP (3.20), the highest strikeout rate (28.7 percent), the fourth-best walk rate (7.3 percent), the fifth-best hard-hit rate (33.4 percent) and the best Statcast™ quality-of-contact mark. Interestingly enough, Houston's starters have thrown the second-most innings (896) and its relievers the second fewest (444), though that's probably due more to how productive and healthy -- only six starts have come outside the original top five -- than in any change in pitching philosophy.
That 28.7 percent strikeout rate, by the way, isn't just the best mark of 2018. It's the highest team strikeout rate of all time. Obviously, that has a lot to do with the strikeout-heavy nature of the sport right now, because each of the Top 20 all-time strikeout seasons have come since 2015. It's still, quietly, a record.

Going back to run prevention, dropping from 4.5 runs per game allowed last year to 3.3 runs per game this year is sizable, and some of it is pretty easily explained by the changes in the Astros' rotation. Last year, they had only five starts from Justin Verlander; this year, it's 32. Last year, Gerrit Cole was merely OK with Pittsburgh, not starring for Houston. No Astros starter had more innings, believe it or not, than Mike Fiers and his 5.22 ERA.
But it's really Houston's bullpen that stands out here, as we pointed out two weeks ago when we declared that its relievers were the best-positioned group for October, just ahead of Oakland, due to talent and depth. Consider this: Last year, the Astros took 11 pitchers into the ALDS against the Red Sox. Let's make a hypothetical 11-man staff for the playoffs this year.
Starters (4)
Verlander, Cole, Charlie Morton, Dallas Keuchel
Relievers (7)
Ryan Pressly, Roberto Osuna, Héctor Rondón, Joe Smith, Collin McHugh, Lance McCullers Jr., Tony Sipp 
Good, right? Now realize that this excludes Will Harris, who has 64 strikeouts in 53 innings. It excludes Brad Peacock and Chris Devenski, two of the team's most important multi-inning relievers of the past two seasons. It doesn't include rookie sensation Josh James , who has 17 strikeouts in 10 2/3 innings while regularly topping triple digits in velocity.
Maybe this isn't the actual 11. Maybe Sipp doesn't make it or McCullers isn't healthy. The point is, very good relievers won't make the cut here. There are just too many, and it's worth noting that Osuna wasn't the team's most impactful July reliever acquisition -- that'd be Pressly, who brought his high-spin curveball to Houston, where he's since put up a 26/1 strikeout/walk ratio.

Now, what about those Red Sox? They're very good, obviously, with a pair of AL MVP Award candidates in Mookie Betts and J.D. Martinez, an ace in Chris Sale and a resurgent David Price. They'll have the most wins and home-field advantage for a reason. Given the difference in team record, why are we giving the edge to the Astros?
It's a little due to the rotation, because the recovering Sale may not yet be at full strength, and the back end of Houston's rotation is stronger than Rick Porcello or Eduardo Rodriguez or Brian Johnson. It's a little due to the stars-and-scrubs nature of the lineup, where the Red Sox have had huge hitting problems at catcher (30th in MLB), second base (25th) and third base (27th). 
You can quibble in either direction on all that. It says here that the difference is going to come in the bullpen, where the Astros may have more talented relievers than they know what to do with, while the Red Sox's relievers have had more than a few rough patches. Let's just look at the bullpen performance of the two teams since Aug. 1, to account for the arrivals of Pressly, Osuna and others.
ERA: Astros 2.50 (1st), Red Sox 3.90 (15th)
Weighted on-base average: Astros .267 (1st), Red Sox .328 (21st)
Strikeout rate: Astros 30 percent (2nd), Red Sox 24.3 percent (10th)
Walk rate: Astros 7.6 percent (4th), Red Sox 10.8 percent (27th)
Hard-hit rate: Astros 33 percent (7th), Red Sox 33.6 percent (9th)
The Astros rank well in everything, obviously, but the problem is that the Red Sox don't. While knuckleballer Steven Wright and rookies Bobby Poyner and Ryan Brasier have been intriguing additions, the trio of Matt Barnes, Heath Hembree and Tyler Thornburg have all struggled in the second half. (After a 3.15 group ERA in the first half, they've put up a 5.60 mark in the second, with Barnes working through a hip issue.) Even Craig Kimbrel has had his issues, walking nearly six per nine since the All-Star Game, though he's still missing plenty of bats.
Maybe Nathan Eovaldi succeeds there, or Drew Pomeranz or Brandon Workman. The point is, Boston's bullpen can't compare to what Houston is bringing, and it's become ever more clear what the postseason is about. You need relievers, good ones, lots of them. The Astros have the edge here and in the rotation, and at worst fight to a draw on offense. They've done this despite something of a lost season from Carlos Correa (.181/.261/.233 in the second half), and poor second halves from Yuli Gurriel and Evan Gattis. They're not without their own issues. 
Now, you might argue that the Red Sox would have home-field advantage in any potential postseason matchup, and that's true. Then again, the Astros have an answer for that, too, with their .703 winning percentage on the road (52-22). Dating back to the start of the "live ball" era in 1920, only two teams have had a better road winning percentage, Joe DiMaggio's 1939 Yankees and those 2001 Mariners.
The Astros won't win the most games this year. In that sense, the road to the World Series still goes through Boston. But Houston is still the defending champion, until it gets dethroned. From this view, the Astros look like the best-positioned team to win it all in 2018. They look like the best team in baseball.