Who has the deepest projected lineup in the Major Leagues headed into 2017? Since you can see the giant headline that's blaring out the answer, we'll assume you already know. The 2017 Houston Astros project to have the deepest lineup in the Majors. They might even end up with the best league-adjusted lineup in team history.
"How does one define deepest?" you might ask, and you'd be correct to do so. "Deepest" doesn't necessarily mean "best," and deepest doesn't guarantee the Astros will score the most runs this year. But what "deepest" does mean is that there's real reason to believe that Houston will have the most above-average hitters of any lineup, and there's real value to that. No, the Astros don't have a Joey Votto, but Votto may be the only above-average hitter the Reds have. Houston, on the other hand, might not have a single true weakness in the lineup. 
So how are we defining this? The only real way to look forward is to use projections, and while they're imperfect, they're the best we have, because you can't simply look at what happened last year and expect that the same thing will happen this year. We'll use 2017 Steamer projections, an advanced system that uses past performance and aging trends to project performance. It's an estimate, but of course anything about a season that hasn't played out yet is an estimate.
We set a minimum of 300 expected plate appearances, and we looked only at hitters projected to be league average or better (i.e., with a projected 100 or higher Weighted Runs Created Plus, or wRC+, a park-adjusted stat that sets 100 as league average). That left us with 146 hitters, or 4.8 per team. In the real world of 2016, there were 150 hitters who had at least 300 plate appearances and a 100 wRC+ or better. This is all coming together perfectly.
From there, it's as simple as breaking down the 146 hitters by 2017 team, setting aside for now the four remaining free agents (Adam Lind, Chris Carter, Mike Napoli and Brandon Moss). A bunch of teams can expect five or six average or better hitters. A few can boast seven. But no one touches the Astros' eight, do they?

That group of eight includes a pretty interesting mix. Obviously, the first three names that come to mind are returning young stars Jose Altuve, George Springer and Carlos Correa. Evan Gattis is the fourth, as his power has outweighed his on-base issues well enough that he's been average or better in each of his four years. Veteran newcomers Josh Reddick and Carlos Beltran are included as well, and the Astros can expect full seasons from Alex Bregman and Yulieski Gurriel, who debuted for the team last year.
Obviously, these aren't perfect numbers. Gurriel is 32 and hit just .262/.292/.385 in part of a season last year, though the projections give him a boost based on his production in Cuba (and he's projected to just squeak in at an average 100 wRC+, anyway). Brian McCann was just barely above average the last two years and has a projection that's just barely below average, not unexpected for a 33-year-old catcher. Last year, the Astros had five of these players, and subtracted Luis Valbuena, who signed with the Angels. They've added, potentially, four more.
That group of eight just edges out the seven from Cleveland (Edwin Encarnacion, Carlos Santana, Jason Kipnis, Michael Brantley, Francisco Lindor, Jose Ramirez and Brandon Guyer), Washington (Bryce Harper, Trea Turner, Anthony Rendon, Adam Eaton, Jayson Werth, Daniel Murphy and Ryan Zimmerman), the Dodgers (Corey Seager, Adrian Gonzalez, Justin Turner, Joc Pederson, Yasiel Puig, Yasmani Grandal and John Forsythe) and Pittsburgh (Starling Marte, Andrew McCutchen, Gregory Polanco, Jungho Kang, John Jaso, Josh Bell and Francisco Cervelli).
Again, this isn't a perfect prediction of what will happen, because no such thing exists, and the number of expected above-average hitters aligns pretty well with what we saw on the field last year. But it does show what the Astros tried to do this offseason, which is to put out a lineup with a competent or better hitter at each spot. There are no black holes here to suck the air out of rallies, and that matters.
Gif: Correa and Gattis go back-to-back for the win
Now let's say it all goes as well as it possibly could. How good can this lineup be? Right now, the same projections see the Astros scoring 4.9 runs per game, the second most behind the Red Sox. That would pale in comparison to the 5.8 runs per game the 2000 Astros of Bagwell and Biggio scored, but of course overall run scoring was much higher across baseball back then, so you couldn't compare the raw number directly. Instead, the better way to do it is to compare Houston's runs per game as a comparison to Major League runs per game that season.
For example, the 2000 Astros weren't the best-scoring team in club history because they scored 5.8 runs per game; they were because compared to the 5.1 runs per game in the sport that year, they were 12.6 percent above average. Last year's Astros scored 4.5 runs per game, and so did Major League teams as a whole, so they were even (0 percent). If the 2017 Astros really do score 4.9 runs per game, and MLB scoring stays steady at 4.5, they'd be 9.4 percent above average. It'd tie 2001 for the third-best mark in team history, behind 2000 and 1998.
That's getting far ahead of ourselves, of course. Projections are just that, not reality. But while there remain questions about the health of the rotation, the Astros have created an extremely talented lineup around a quietly very good bullpen. It might not be the best lineup in baseball; it could, however, be the deepest. That might just be good enough.