What's the best lineup for the next 5 years?
Catcher: Buster Posey, Giants
The reigning NL MVP is hitting .311/.379/.485 for his career, and at age 26, it just hitting his prime now. That age is the tiebreaker between the other two top catchers in the game. Joe Mauer might be the most underappreciated player in the game, but he's 30 now and has enough of an injury history that his time behind the plate is likely numbered. Yadier Molina is the best defensive catcher in baseball, but is 31 now. Posey from ages 26-30 is likely a better bet than Mauer or Molina into their mid-30s.
First Base: Miguel Cabrera, Tigers
Yeah, he's a third baseman right now, but so what? He's not great defensively at the hot corner, and moving him across the diamond to the easier position will lower the defensive liability. Of course, you don't pick Cabrera for his defense. Joey Votto would also be a great pick, and with his career .418 OBP, I'm surprised myself I'm not picking him. There's also the two guys having breakout years at first base: Paul Goldschmidt and Chris Davis. Goldschmidt is the youngest of all these guys at 25, so he might be the safest best. However, Cabrera is somehow hitting better this year than he did in last year's Triple Crown and MVP winning campaign. He's one of the best hitters ever at the peak of his powers. I'll take the gamble that 2018 Miguel Cabrera is a reasonable facsimile of 2013 Miguel Cabrera.
Second Base: Jason Kipnis, Indians
No Cano? No Pedroia? Am I insane? Maybe, but hear me out. Kipnis is having a breakout year, hitting .292/.371/.481. His 142 OPS+ is better than both (139) and Pedroia (111) this season. Even more importantly, Kipnis is still just 26 and right in his prime. Cano and Pedroia are both 30, and second basemen tend to decline quickly once they hit the wrong side of that number. Cano is the best second baseman right now, but over the next 5 years, Kipnis is the good bet to be better.
Shortstop: Manny Machado, Orioles
The defensive highlights keep piling up for Machado at third base. That just makes me more and more excited for when Machado is moved back to his original position. Manny's defense has been a revelation from the start, while his bat is starting to come around in the majors. He continues to lead the league in doubles with 43, although he's cooled off in that regard. He still needs to start walking more to be a real offensive force, but he turned 21 last month, so there's still time for that, and for some of the doubles to start turning into home runs. If it's seems presumptuous to put at short a guy who hasn't actually played there yet, look at the list of current shortstops. Not a superstar among them. If I had to pick a current shortstop, it would be Andrelton Simmons. He'll probably never hit all that much, but his glove is truly special.
Third Base: Evan Longoria, Rays
With Cabrera and Machado moved to other position, this becomes a battle between Longoria and David Wright, with apologies to Adrian Beltre (34 is way too old to be considered). Wright's career line is .301/.382/.506, Longoria's .275/.358/.513. Longoria appears to have the edge defensively. More importantly, Longoria is 27; Wright is 30. That's what gives it to Longo.
Turn to the next page for the outfielders and pitchers.