Position by position: These are the biggest upgrades

With only about a month left before pitchers and catchers report to Spring Training, plenty of potential contenders still have needs to address, and some high-profile free agents remain available.
Still, as quiet as the offseason has seemed at times, there have been some important additions. With that in mind, here is a position-by-position look at which teams have done the most to upgrade weak spots, taking into account both their 2018 production (or lack thereof) and '19 outlook:
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Catcher: Brewers
The Mets and Nationals certainly deserve mention here as well, after New York landed Wilson Ramos and Washington brought in a combo of Yan Gomes and Kurt Suzuki. But Milwaukee sits on top because Yasmani Grandal -- who agreed to a one-year deal Thursday -- has easily the highest ceiling, as a true two-way contributor, in that group. His unfortunate postseason scuffles aside, Grandal has been an above-average hitter in every season of his career (117 wRC+) and is one of the game's top pitch framers. Given that Brewers catchers (mainly Manny Piña and Erik Kratz) hit .237/.294/.363 last year, Grandal provides far more upside.

First base: Rockies
In 2018, Colorado first basemen (primarily Ian Desmond) finished 28th in the Majors in wRC+ (80) and 29th in FanGraphs' wins above replacement (-1.2), even as the team battled its way into the postseason. Signing veteran Daniel Murphy to a two-year contract was a bit of a risk, given that the left-handed batter will be 34 next season and struggled early in '18 as he came back from a knee injury. But Murphy was one of the game's top hitters from 2016-17 and recovered to slash .315/.346/.498 after the All-Star break. He should be a lot more comfortable defensively after moving from second to first.
Second base: Nationals
It's been a productive offseason for Washington, which has addressed several areas of need -- even with the Bryce Harper situation unresolved. One of the those was the keystone. Last year, Murphy's injury, slow start, and defensive shortcomings limited the club's production at second. Howie Kendrick was lost for the season in May, and Wilmer Difo posted a .650 OPS. Now the Nats have made a low-risk rebound bet by reaching a one-year agreement with Brian Dozier. One of MLB's best second basemen from 2013-17, Dozier slumped last year while fighting a knee issue. Steamer projects a solid 2.6 WAR in '19, and a fully healthy Dozier could contribute with the bat and glove while allowing Kendrick and Difo to come off the bench.

Third base: Braves
This one may change when we learn where Manny Machado winds up. In the meantime, this selection admittedly doesn't quite fit here, because the hot corner actually was a highly productive spot for the 2018 Braves. Behind a strong year from Johan Camargo, the National League East champs got a 116 wRC+ and 4.3 WAR from their third basemen. With that said, free-agent acquisition Josh Donaldson has the much more robust track record and the much more optimistic projections, with the upside of one of the league's elite third basemen. Meanwhile, Camargo now can see time around the diamond.
Shortstop: Phillies
The baseball world waits to see whether Philly lands one of the offseason's big fish -- Harper or Machado. In the meantime, pulling off a trade with the Mariners for shortstop Jean Segura was a meaningful upgrade for a club looking to take the next step. The 2018 Phillies ranked 27th in wRC+ (75) and 28th in WAR (0.8) from shortstop, with youngsters J.P. Crawford and Scott Kingery struggling mightily with the bat before veteran Asdrúbal Cabrera arrived at the Trade Deadline. Now Cabrera is a free agent, Crawford is in Seattle and Kingery can move around the field, while Segura stabilizes short with an above-average bat and solid defense.
Outfield: Mariners
It might seem strange to have the Mariners here, in an offseason that has seen them lose Segura and several other key pieces. At the same time, Seattle has complemented rising star Mitch Haniger with Mallex Smith and Domingo Santana, with the former pushing Dee Gordon back to second base and the latter replacing Denard Span and several others. The Mariners, who got little production from center or left last year, also now have Jay Bruce in the mix. But the speedy Smith and talented Santana -- who was blocked in Milwaukee -- look like the biggest prizes and both have at least three years of club control remaining.
Designated hitter: Twins
Minnesota was below replacement level at DH last year, ranking second-to-last in the AL in OPS (.682) and home runs (15). The Twins used 14 players in that role, including three for at least 35 starts: Logan Morrison, Joe Mauer and Robbie Grossman. That trio is gone, with Nelson Cruz now likely to see the vast majority of the at-bats at DH. Cruz, who signed a one-year deal with a club option, leads the Majors with 203 homers over the past five seasons and is tied for fifth with a 145 wRC+. His power could help Minnesota make a run at Cleveland in the AL Central.

Starting rotation: Reds
Cincinnati may not be done improving in this area, with a free agent such as Dallas Keuchel or a trade target such as Sonny Gray among the possibilities. But the Reds already have made a pair of moves to solidify a rotation that last year posted the sixth-highest ERA and fourth-highest FIP in the Majors, over the eighth-fewest innings. Of the six Reds who made at least 20 starts last year, none had an ERA below 4.30. However, Homer Bailey (6.09) and Matt Harvey (4.50) are out, and Sal Romano (5.48) likely has been bumped, with Cincinnati trading for Nationals righty Tanner Roark and Dodgers lefty Alex Wood. While both are due to reach free agency after 2019, Roark has been a reliable innings-eater, and Wood owns a career 3.33 ERA as a starter.
Bullpen: Mets
Several clubs have added relief talent, even as Craig Kimbrel, Adam Ottavino and others remain unsigned. But the Mets -- who have been quite busy this offseason -- stand at the top of the heap after landing Edwin Díaz from Seattle. Diaz was arguably the best reliever in the Majors in 2018, with a 1.96 ERA, 57 saves and 124 strikeouts in 73 1/3 innings. The hard-throwing 24-year-old can team up with Jeurys Familia, who re-signed for three years after getting shipped to Oakland ahead of the 2018 Trade Deadline. A full season from both righties would do wonders for a Mets bullpen that ranked 28th in the Majors in ERA, 29th in FIP and 23rd in strikeout rate. New York also inked a Minor League deal with southpaw Luis Avilán, who has held lefties to a .581 OPS in his career.