Player A is Nomar Garciaparra, through his age 29 season (2003).
Player B is Troy Tulowitzki, also through his age 29 season (current).
These two players are often talked about together, and for good reason. Not only are they statistically similar, they both have another (unfortunate) thing in common: injuries. Injury prone players often make coaches (and fans) very nervous once they hit age 30. Garciaparra is somewhat of a poster boy for this, as he was only able to accrue 1940 more plate appearances over five seasons after age 30, before bowing out at age 35. While his production only dropped slightly (he hit .291/.343/.446 in that span) his inability to stay on the field turned a once promising Hall of Fame career into a big game of what-if.
Fans in Colorado have to wonder the same thing about their fan favorite at shortstop. Every year there is talk about the Rockies trading Tulo away, but it has yet to happen. The fans there love Tulo, but one has to wonder if his previous injury problems will catch up to him in a big way. Tulowitzki put up a 5.5 WAR just last year alone, so it seems likely that he will eclipse the 3.0 WAR that Garciaparra put up in his 30's. However, his value might not get much higher than it is right now, and the glut of prospects the Rockies could get in return may make it worth it.
It felt like robbery when the baseball world was not able to see a healthy Nomar in his 30's. His prime was as good or better than Alex Rodriguez and Derek Jeter, and without injuries he could have had a career that cemented himself as one of the best hitting shortstops of all time. Even with his injury-riddled 30's, Garciaparra still got 5.5% of the BBWAA voters to vote for him as a HOFer, meaning he will get to stay on the Hall of Fame ballot for next year.
Tulowitzki could be baseball's redemption for our loss of Nomar. If he is able to fight off the injury bug, his career could take the path that we know Nomar's could have, vaulting him into the ranks as one of the better shortstops the game has ever seen, and earning him the plaque that Nomar should have earned. Of course, this is a massive if, for a few reasons. One - as we look at the stats above, they are indeed comparable but Nomar is better in nearly every category. So even if Tulo is able to continue to play, he may not be what Nomar could have been. Again though, he could more than make up for that in his 30's. The big if is of course the injuries. If Tulo can stay healthy, his ceiling could reach the upper echelon of big, power hitting shortstops. The Alan Trammell, Barry Larkin, Nomar Garciaparra prototype could live on through a guy like Tulo (although comparing him to the games greatest (clean) power hitting SS, Cal Ripken Jr, seems comical because of his "iron man" reputation).
I hope Troy Tulowitzki can stay healthy and show us the Garciaparra that we never had, if only because I hate seeing careers derailed by injuries. No one likes the what-if game.