Head of the class: Best free agents at each position

As September begins, there is still plenty of baseball left to be played this season, but it's never too early to look ahead to the Hot Stove.
This coming offseason won't feature the most high-profile group of free agents, with perhaps the biggest name coming off the board when All-Star pitcher Stephen Strasburg signed a long-term extension with the Nationals in May. The middle-infield spots in particular lack depth, but there still should be plenty of appealing options for clubs looking to add pieces over the offseason.
Here then is preview of the upcoming free-agent class, highlighting the top available players at each position based on their 2016 wins above replacement (WAR), according to Baseball Reference.
CATCHER
Wilson Ramos, Nationals (2.7 WAR): He has stayed healthy for a second straight season and been one of the game's most improved hitters.
Carlos Ruiz, Dodgers (1.6 WAR): Recently acquired by L.A., the respected veteran could end up back there, thanks to his $4.5 million club option.
Jason Castro, Astros (1.2 WAR): The left-handed batter has a career .547 OPS against southpaws, but he has hit righties effectively (.772 OPS this season).
Others of note:Matt Wieters (0.4 WAR) has posted a sub-.700 OPS after accepting the Orioles' one-year qualifying offer last offseason. He could be joined in free agency by experienced veterans such as Alex Avila, Kurt Suzuki and Chris Iannetta, who has a club option for 2017.

FIRST BASE
Edwin Encarnación, Blue Jays (3.3 WAR): He turns 34 in January and has spent a lot of time at DH, but he leads the American League in RBIs and is second in homers.
Steve Pearce, Orioles (2.4 WAR): The versatile veteran also has spent time at second, third and both corner outfield spots this season, while slugging better than .500.
Mitch Moreland, Rangers (1.8 WAR): His roughly league-average 103 OPS+ in 2016 is right at his career total over seven seasons.
Others of note:Carlos Santana ($12 million club option) may not join this group, but sluggers such as Brandon Moss, Mike Napoli and Adam Lind will be available, along with DH types Pedro Álvarez and Kendrys Morales. Mark Trumbo will also be on the market, but his lack of defensive value has limited him to 1.0 WAR despite his 40 homers.

SECOND BASE
Neil Walker, Mets (2.5 WAR): He has tied or set career highs in homers (23) and slugging (.476), but he now appears headed for season-ending back surgery.
Chase Utley, Dodgers (1.6 WAR): He has held his own as L.A.'s regular leadoff man in his age-37 season.
Kelly Johnson, Mets (0.6 WAR): After producing negative WAR with the Braves, Johnson has come up big since a June trade to New York.
Others of note: There isn't much depth here, but Chris Coghlan, Daniel Descalso and Stephen Drew all have experience at the position.
THIRD BASE
Justin Turner, Dodgers (4.2 WAR): He has been one of the 20 most effective hitters in MLB since 2014, overcoming a slow start this season.
Martín Prado, Marlins (3.6 WAR): The 32-year-old is putting up his best slash line since 2010, batting .319/.371/.432.
Luis Valbuena, Astros (2.6 WAR): Before suffering a season-ending hamstring injury in late July, Valbuena excelled against right-handed pitchers, as usual (.841 OPS).
Others of note: With David Freese signing an extension with the Pirates and the Angels holding a $7 million option on Yunel Escobar, that leaves Aaron Hill, who has struggled since a trade to the Red Sox.

SHORTSTOP
Names to note: Unless Ian Desmond returns from his successful transition to the outfield, options here are extremely limited. Among primary shortstops who are potential free agents, only the Royals' Alcides Escobar has a positive WAR value (0.4), and he has an affordable $6.5 million club option for 2017. Erick Aybar and Alexei Ramirez are veterans who will be coming off rough seasons, barring a huge late surge.
CORNER OUTFIELD
Yoenis Céspedes, Mets (2.8 WAR): Given his .298/.369/.572 line with 27 homers, it seems likely that Cespedes -- who also plays a lot of center -- will opt out of his current deal. If so, he will likely be viewed as the top free agent on the market.
Michael Saunders, Blue Jays (2.4 WAR): After playing a total of 87 games over the past two years, Saunders is taking advantage of his good health in 2016.
Colby Rasmus, Astros (2.0 WAR): Rasmus' bat has been anemic in the second half, but most of his WAR value this season has come from his defense.
Others of note: Trumbo leads the Majors with 40 home runs, but he has not fared well with defensive metrics. José Bautista, Carlos Beltrán, Jay Bruce, Matt Holliday ($17 million club option) and Josh Reddick all are accomplished players, and Matt Joyce and Ángel Pagán have enjoyed productive rebound years.

CENTER FIELD
Dexter Fowler, Cubs (3.2 WAR): After returning to Chicago on an $8 million deal with a $9 million mutual option for 2017, Fowler is enjoying a career year despite a month lost to injury.
Desmond, Rangers (3.0 WAR): He should find a more favorable market this offseason, as he sits on the brink of a fourth 20-20 season.
Cameron Maybin, Tigers (1.4 WAR): In spite of multiple DL stints, including one that held him out until mid-May, Maybin is putting together his best year since 2012.
Others of note:Rajai Davis leads the AL with 34 steals at age 35, while Coco Crisp, Austin Jackson and Jon Jay also will be available. For Carlos Gómez, a lot could depend on how he performs for the Rangers down the stretch.

STARTING PITCHERS
Rich Hill, Dodgers (3.2 WAR): The 36-year-old's ERA (2.09) is tied for MLB's second lowest (minimum 80 innings), but blister issues have limited him to six innings since July 7.
Colby Lewis, Rangers (3.2 WAR): Lewis, who recently turned 37, has a 3.21 ERA in 15 starts and could return soon from a lat strain that has held him out since late June.
Bartolo Colon, Mets (2.5 WAR): He's still going strong at age 43, throwing more than 150 innings with a 3.44 ERA.
Jeremy Hellickson, Phillies (2.5 WAR): His 3.80 ERA is easily his best since 2012, although his peripheral numbers haven't changed much.
Iván Nova, Pirates (1.6 WAR): He has accrued more value in 31 1/3 productive innings with the Bucs than he did in 97 1/3 innings with the Yankees.
Others of note:Jaime García, Gio González and Jason Hammel all seem likely to be retained with club options, while Scott Kazmir and James Shields may choose not to exercise their opt-out clauses. Clay Buchholz ($13.5 million club option), Derek Holland ($11 million club option), Jonathon Niese ($10 million club option) and Edinson Vólquez ($10 million mutual option) could be more likely to hit the market, along with a group that includes Brett Anderson, Andrew Cashner, Jorge De La Rosa, R.A. Dickey, Doug Fister, Ryan Vogelsong and Jered Weaver.

RELIEF PITCHERS
Mark Melancon, Nationals (2.3 WAR): The righty is 121-for-130 in save chances with a 1.86 ERA since 2014.
Kenley Jansen, Dodgers (2.1 WAR): He has struck out at least 13 batters per nine innings with a FIP no higher than 2.40 in every season of his career.
Aroldis Chapman, Cubs (1.9 WAR): Nobody hurls triple-digit heat like Chapman, whose 13.5 strikeouts per nine nine is actually his lowest mark since 2011.
Others of note: Relief pitching is probably the deepest aspect of this free-agent class. Wade Davis, Jason Grilli, Seunghwan Oh and Fernando Rodney all could have options picked up, but fellow right-handers such as Joe Blanton, Santiago Casilla, Neftalí Feliz, Jonathan Papelbon, Sergio Romo, Joe Smith, Koji Uehara and Brad Ziegler should be available. Brett Cecil, Boone Logan and Javier López are among the southpaws headed for free agency.