The case for JJ
With 83 saves and a 162 ERA+ since signing with the Diamondbacks three seasons ago, J.J. Putz has been one of the most effective closers in the majors - only Craig Kimbrel has had more saves and a better ERA+. Even last season, when injury took him out of the closer's spot, and Brad Ziegler's success prevented Putz from regaining it, he still put up a 2.36 ERA and struck out 10 batters per nine innings. JJ is already second on the all-time franchise list for saves, and with only 15 separating him from leader Jose Valverde, given good health, he should easily overtake Papa Grande this year, given the chances.
Providing veteran leadership in the bullpen, Putz is due to earn $7 million this year. While it's true that games sometimes need to be saved before the ninth, that's never been the way manager Kirk Gibson has worked, and that price would make Putz extremely expensive for any other role apart from the closer's. He will become a free-agent in 2015, and while it's likely Reed will take over then, one advantage of using Putz in the ninth this campaign, is that it will help to keep Addison's costs down as he goes through arbitration, beginning next year. Look at Kimbrel: as the Braves' established closer, he's asking for $9 million in his first year of eligibility.
The case for Addison
We saw last year one of the problems with Putz: he is injury-prone. While we were able to get through without major issues in 2011-12, over the past six seasons, JJ has averaged 46 innings per year, which is well short of what you would want from an everyday closer. In contrast, since going full-time at the start of 2011, Reed has averaged 71 innings between the majors and minors, with not even a whisper of any health concerns. Youth is also obviously on his side: Reed only turned 25 in December, while Putz will enjoy his 37th birthday later this month.
Yes, last season, Reed did have an ERA considerably higher than Putz (3.79 to 2.36). However, if you take defense out of the equation, FIP tells a different story, with Reed having the better year (3.17 to 3.83). That's reflected in a STEAMER projection for 2014 which has Reed with a 3.10 ERA, compared to Putz's 3.22. Of particular concern, Putz's walk rate spiked significantly last year, going up from 1.8 per nine IP, all the way to 4.5. Both Reed's strikeout and walk rates were very close to the 2012 numbers, so it appears he has the more consistent peripherals, making his performance projectable with a greater degree of certainty.
The spring outlook
We should be able to get a handle on this over the course of Cactus League play, though I'd caution against reading too much into early save opportunities. Putz has always been cautious with his arm in pre-season play; aware of his age, he apparently prefers to "save his bullets" for the regular season. In both 2012 and 2013, he threw only 5.1 innings in game situations, and didn't appear at all until March 13 last spring. However, there was talk in September of a new approach, Gibson saying, "We'll take a little different attack in Spring Training -- he'll throw a little more.. It just seems like when he throws more, he gets stronger. So he'll be in more games and stuff before the season."
There is still a slight possibility the issue resolves itself with a trade. Over the winter, there has been speculation both players might be moved. At the time he arrived in Arizona, Bob Nightengale Tweeted, "Several #MLB executives say they wouldn't be surprised to see #Dbacks spin off Addison Reed in future trade for top tier starter," and that's a need the Diamondbacks never subsequently filled. As for Putz, there was some speculation in January he could be dealt to the Yankees, in exchange for Ichiro - a trade of mutually expendable players, each in the last year of their contracts. However, with days until pitchers report for us, a deal seems less likely.
I think it'll be Putz who starts the season in the role, but if he falters, or his health isn't up to scratch, I suspect Gibson will not give him a long leash [though the contract extension announced yesterday may help to dilute the "win now" imperative a bit]. But here's a dark-horse bet: don't count our David Hernandez either. Especially if he can show that last year's mid-season meltdown was a blip, and the real DH was the one who posted an 0.64 ERA and held batters to a .130 average on his return from Reno.