With the recent departure of Adam Dunn, the Nationals are now weighing their options to replace the Big Man's offense and defense (mostly offense) at first base. The three potential replacements being discussed are Adam LaRoche, Carlos Peña, and Lance Berkman (these are at least the guys being discussed by us-it seems the Nationals have been mainly pursuing LaRoche and Peña).
LaRoche, the youngest of the bunch though still 30, sported a .339 wOBA last year along with the best fielding rating of the group. His wOBA over the last three years, however, is the lowest of the group (around .350, his career mark) and his career UZR/150 is second lowest (-2.6), though the difference between the three is fairly small (Peña has a -2.7, Berkman a 3.1). LaRoche also has the least plate discipline in that he walks the least, and he also has the least power. Because of his weak offensive abilities LaRoche will likely be the cheapest option for the Nats, although his agent may be looking for a long-term contract. In that case, LaRoche looks less attractive than the others as his wOBA seems to be sustained more by his strong BABIP (.315 career) and less by walks and power, the two things that players seem to retain best into old age.
Carlos Peña, 32, had his worst offensive season ever this year, with a career low .326 wOBA. Peña did, however, maintain his astoundingly high HR/FB ratio (20.5% career) and his equally impressive BB% (above 15% since 2007 except this season when it was 14.9%). The precipitous decline in his wOBA (.360 career) last year likely came from his absolutely abysmal BABIP of .222. I'm going to guess that this BABIP is explained by the fact that Peña was a ground ball machine last year (44.9% of his balls in play were on the ground last year compared to 36.9%) though he did do the same thing in 2006 and had a BABIP of .364. (I guess Peña hitting below the Mendoza line this year was God's way of evening things out.) Though players like Peña seem to command large contracts because of their power, Peña's horrifying average will probably keep the price down. If he stops his ground ball frenzy next season and ends up with a wOBA close to what he had in 2007-2009 (around .390) when he started walking a lot, he could end up being a quite capable replacement for Adam Dunn (about .385 wOBA over the last three years).
Lance Berkman could also prove to be a good deal. His power numbers took a significant drop last year, as Berkman ended with his lowest full season wOBA ever and his lowest HR/FB rate for the years for which data is available (there is no data for Berkman's first three seasons). Yet those in the know are attributing Berkman's power decline to his knee injury earlier in the year. Berkman's discipline held steady last year (16% BB%, higher than Peña and LaRoche) and his wOBA was still better than LaRoche's and Peña's. If Berkman returns to recent form, we can expect a wOBA a little above .390 from him. But he will be 35, and at that age knee injuries seem like they don't go away that easily.
Not long ago, we made a case for Berkman as the guy the Nats should be pursuing, but I am now going to argue that things are much closer than they may first appear. Of the three players, LaRoche is the safest gamble in that he seems to be the most consistent. His wOBA will probably be around .350 driven by BABIP and without much power. (To give some context, a .350 wOBA would've been 13th out of 25 of all "qualified" first basemen this year; .390 would've been good for 5th.) Peña and Berkman are the more seductive choices because of their superior power and plate discipline numbers, but they are also riskier because of Peña's inconsistency and Berkman's questionable knee. Also, since none of these three are particularly good long-term commitments (LaRoche because of his reliance on BABIP and his age, Peña because of his age, and Berkman because of his age and injury), the Nationals should not sign any of them to an extended deal.
Assuming each player is seeking a short-term deal, I think that though LaRoche will be the cheapest, Peña and Berkman will be worth the gamble to the Nationals (they need the power), leaving LaRoche out of the picture. Peña and Berkman may be seeking similarly priced contracts as well, since they are comparable offensively and both will have question-marks (for Peña his batting average, for Berkman his knee and age) keeping their contract values down relative to guys with similar power numbers. Then it becomes a question of whether you believe more strongly that Peña's shockingly low BABIP last year was a fluke or that Berkman's knee troubles are behind him. I'd rather take the guy who seemed to have been hit by bad luck than the guy with the physical problem but that's just my gut; let's hope we can trust Mike Rizzo's.