I mean, objectively the answer is Mike Trout right? Not only is he the best player in baseball, but his timeline works perfectly with the Nationals: you want somebody who is really good, but only from 2012 to the present, so he doesn't get in the way of the rebuild.
But that's a boring answer. I'll go with whoever was the best closer in baseball in 2012. Craig Kimbrel won the Rolaids Relief Man of the Year award that year. I don't know if Axford was still good, I remember really liking his facial hair.
I don't know how you fix the 2014 team by adding just one player, that was another really good team that lost in the NLDS. Again Trout would have been useful.
