Although the defending champion Cubs got off to a disappointing start, they made up for it in the second half of the season, posting a 49-25 post-All-Star record that was second only to Cleveland in the Major Leagues. Of course, the Nationals had the fourth-best second-half record themselves, at 45-29, and led the National League East for all but three days of the season. That's despite a leaky first-half bullpen and injuries that took out -- at various times -- their shortstop and their entire starting outfield.
Now, both sides are dealing with hamstring injuries to ace starting pitchers, and what we're left with is an extremely compelling National League Division Series matchup, starting tonight at Nationals Park. But which side has the edge? Let's check it out, position by position.
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(Batting numbers are presented with traditional BA/OBP/SLG and Weighted Runs Created Plus, or wRC+, a park- and league-adjusted number where 100 is set as "league average" for easy comparison.)
Catcher 
Some of these spots will be tough to call, but this one is really, really easy. Cubs catchers combined to hit .275/.361/.467 (116 wRC+), the second best in the Majors, while Nationals catchers, primarily Matt Wieters and Jose Lobaton, hit only .211/.276/.320 (53 wRC+), the weakest line in the game. For the Cubs, that's mostly thanks to Willson Contreras (.276/.356/.499, 121 wRC+) blossoming into a star, but it's worth noting that backup Alex Avila compiled the big leagues' fourth-best hard-hit rate. He's got one of the strongest catcher's throwing arms, too.
Advantage: Cubs
First Base 
Ryan Zimmerman stayed healthy and put together a huge comeback season, recording a .303/.358/.573 (138 wRC+) slash line that was essentially equal to that of Anthony Rizzo (.273/.392/.507, 133 wRC+), hitting for more power than Rizzo did while getting on base less often. We're giving Rizzo a slight edge here because he's a much better defender and his track record is stronger, but with Zimmerman hitting like this, it's really not a big edge.
Slight advantage: Cubs

Second Base 
The Cubs have four different players who could see time here, though it's more likely you'll see Javier Baez or Benjamin Zobrist rather than Ian Happ or Thomas La Stella. Zobrist (.232/.318/.375, 82 wRC+) never really got on track this year, and Baez (.273/.317/.480, 98 wRC+) had more or less the same year he always has, just with some added power. (He was also much better in the second half, hitting .291/.340/.511, 113 wRC+.) Yet while there's a lot of talent in that group, Washington's Daniel Murphy (.322/.384/.543, 136 wRC+) had another outstanding season, making his third All-Star team and posting the Majors' seventh-best contact rate, giving the Nationals an edge here. 
Advantage: Nationals

 Shortstop
Addison Russell was a popular breakout pick this year, but he took a step back in most categories (.239/.304/.418, 84 wRC+), then missed more than a month with a foot injury as Baez stepped in. Trea Turner was also a popular breakout pick in what was expected to be his first full season, but he missed two months after breaking his left wrist when Cubs reliever Pedro Strop hit him with a pitch in late June. Despite playing only 98 games, Turner still stole 46 bases (a club record), and if his .284/.338/.451 (105 wRC+) didn't quite live up to the promise of his 2016 debut, it still gives him the edge here.
Advantage: Nationals

Third Base
Both the Cubs and the Nationals have superstar third basemen who are deserving candidates for the NL Most Valuable Player Award, so yes, this one's a tie. Good luck trying to choose between Anthony Rendon (.301/.403/.533, 142 wRC+) or Kristopher Bryant (.295/.409/.537, 146 wRC+) and their nearly identical stat lines. Any slight edges to one would be counteracted by slight edges to the other, so this one stays a toss-up.
Advantage: Tie
 Left Field
Though Kyle Schwarber's season got off to a pretty disappointing start -- he was hitting just .171/.295/.378 (77 wRC+) when the Cubs optioned him to Triple-A in June -- he has been far more in line with expectations since returning in July, hitting 18 homers to go with a solid .255/.338/.565 (131 wRC+) line. He's still vulnerable to lefty pitching and isn't a strong defender, so expect to see some Jonathan Jay, Happ and Zobrist out here as well. That group has the edge over the Nationals, who will either start 38-year-old Jayson Werth coming off an injury-plagued down season (.226/.322/.393, 88 wRC+) or defensively limited 34-year-old veterans Adam Lind and Howie Kendrick.
Advantage: Cubs

 Center Field
This was supposed to be Adam Eaton, but when he was lost for the year with an April knee injury, Michael A. Taylor stepped in admirably. Taylor put up a slightly above-average line of .271/.320/.486 (105 wRC+), which is about the same as the Cubs' duo of Jay and Albert Almora Jr. managed (.296/.359/.406, 102 wRC+). The Nationals get the edge here, however, because Taylor provided excellent defense, easily the best of these three, and because 20-year-old rookie Victor Robles could step in to offer some of the most elite speed in the Majors.
Advantage: Nationals

 Right Field
Bryce Harper mashed yet again (.319/.413/.595, 156 wRC+), while Jason Heyward struggled (.259/.326/.389, 88 wRC+), and really, that ought to be the end of this discussion. Now, it's a little more complicated than that, since Harper injured his knee in a scary-looking stumble in early August, and he returned in time only to collect three singles in 20 plate appearances during the final week. And Heyward, it should be noted, remained an elite defensive outfielder, adding more value on defense than Harper, so the health and fielding issues offer at least some favor for Heyward. But Harper, when he's right, is one of the most talented sluggers in the big leagues -- and the Nationals need him to be right.
Advantage: Nationals

 Starting Pitchers
Let's start with the uncertainty on both sides, given that Max Scherzer and Jacob Arrieta are each dealing with right hamstring strains, and Arrieta won't appear until Game 4 because of it. What we do know is that Kyle Hendricks will face Stephen Strasburg in Game 1, and don't be fooled by Hendricks' misleading 7-5 record; since he returned from injury on July 24, he has a sparkling 2.19 ERA in 13 starts. Still, the Nats have a slight edge here, because Strasburg, Scherzer, and Giovany Gonzalez (2.96 ERA) may be three of the top five names in the NL Cy Young Award voting, and Tanner Roark is a perfectly capable fourth starter. While Hendricks and Jose Quintana have been solid, Jonathan Lester posted a 5.51 ERA over the last two months, and Arrieta could be limited. Both sides have good rotations; Washington's is just slightly better -- if, that is, Scherzer can go.
Advantage: Nationals

 Relief Pitchers
The Washington bullpen was a tremendous problem for most of the season, though summer acquisitions Sean Doolittle, Ryan Madson, and Brandon Kintzler added considerable value, helping the Nats' bullpen go from a worst-in-baseball 5.30 relief ERA in the first half to a much better 3.54 in the second half. Doolittle has been great, but Kintzler (12 whiffs in 26 innings) has been just OK. On the other side, Wade Davis (2.30 ERA, 79 whiffs in 58 2/3 innings) looks like he did when he was starring for the Royals, Brian Duensing (61 strikeouts in 62 1/3 innings, 2.74 ERA) has been shockingly good and C.J. Edwards, Strop and Mike Montgomery remain weapons. They may even be joined by John Lackey, which is entertaining. It's only a small edge here for Chicago, though.
Advantage: Cubs