Yesterday morning we learned quite a bit about the free agent reliever market, specifically that the Yankees are in “serious pursuit” of Andrew Miller and are unwilling to give David Robertson a four-year deal. They’ve reportedly talked about trades involving bullpen help with the Marlins and Braves as well. The Miller and Robertson stuff is the big news though. It sure feels like one of those two will wear pinstripes next season.

As I said yesterday, I think the Robertson stuff is all posturing and they’re just trying to get his price down. The interest in Miller could be an attempt to apply some pressure as well. It goes without saying that both Robertson and Miller are excellent pitchers anyone would love to have in their bullpen. It makes perfect sense that the Yankees would have interest in both guys. But it sounds like it will only be one or the other, not both as much as I and everyone else would love it. Is one a better investment than the other? Let’s compare.

Recent Performance

Again, both Robertson and Miller are excellent. They’re elite relievers in the prime of their careers. Here are their 2014 seasons side-by-side:

Miller was better than Robertson this past season in nearly every way. The only thing Robertson did better was get left-handed batters out, which is pretty amazing because he’s a righty and Miller’s the lefty with the all-world slider. Robertson’s cutter and curveball are really great in their own right too.

The difference between these two guys this year is that Miller never had a season this good before and Robertson hadn’t had one this bad — “bad” — since 2010, before his breakout 2011 effort. Robertson’s been dynamite for four years now. Miller spent a very long time trying to figure out his mechanics — he had a 5.54 ERA (5.12 FIP) as recently as 2011 — and it wasn’t until last year that he turned into a super reliever. He was very good in 2012 (3.35 ERA and 3.27 FIP), but 2013 was when he joined the tier of relievers Robertson has occupied since 2011.

Here are Robertson and Miller’s performances side-by-side over the last three years:

Nearly identical. Miller has a slight edge in strikeout rate, Robertson a slight edge in walk rate. Miller’s platoon split is smaller. And, of course, Robertson has thrown more than 40% more innings. That’s not negligible. If we were to take Miller’s last ~190 innings to match Robertson’s total instead of the last three years, he’d have a 3.54 ERA and 3.27 FIP. (If we took Robertson’s last ~130 innings to match Miller’s total, he’d have a 2.55 ERA and 2.65 FIP.)

In the middle of the 2012 season, Robertson simply stopped walking guys. It was weird and pretty awesome. Throwing strikes was never his strong suit, but, out of the blue, he started pounding the zone and has done so since. Miller went through something similar that season though not as extreme. His walk problems were also much more severe than Robertson’s earlier in their careers:

Source: FanGraphs — Andrew Miller, David Robertson

Long story short, Miller was better than Robertson in 2014 but Robertson’s track record as a top notch relief pitcher is nearly twice as long in terms of innings pitched. I think it’s pretty interesting Robertson has been better against lefties than Miller while Miller has been better against righties than Robertson. There’s a weird reverse platoon split thing going on.

Stuff Breakdown

Since they are relievers, it’s no surprise Robertson and Miller are basically two-pitch pitchers. They will both throw the occasional changeup but not often enough to be a factor. Robertson is a cutter/curveball pitcher — he’s all but abandoned the four-seam fastball in favor of the cutter at this point — while Miller is a four-seamer/slider pitcher. With an assist from Brooks Baseball, here is a comparison of their fastballs (FB) and breaking balls (BB).

Whiff+ and GB+ are the swing-and-miss and ground ball rates of the individual pitches relative to the league average. It works like wRC+ and ERA+ and all that. 100 is average, the higher the number, the better. Got it? Good.

It surprised me that Robertson’s cutter has been comfortably below-average at getting swings and misses, though I do suppose he gets a lot of called strikes with the pitch. Miller has the much better fastball in almost every way — velocity, swings and misses, and grounders — but Robertson’s curve is the better breaking ball when it comes to getting empty swings. Miller’s slider has a small advantage at getting ground balls.

So, I guess the best way to explain this is Miller has the more dominant two-pitch mix but Robertson has the best individual pitch with his curveball. That make sense? Curveballs historically have a much smaller platoon split than sliders, but Miller’s slider is so damn good it doesn’t matter what side of the plate the hitter is on. He’s a lefty and that’s nice, but he’s far from a lefty specialist.

Injury History

Robertson and Miller are the same age — Robertson is 42 days older — and neither has had any kind of major arm injury, so that’s good. Robertson missed two weeks with elbow stiffness back in September 2009 but hasn’t had any trouble since. He’s been on the DL only twice in his career: 33 days for an oblique strain in 2012 and 15 days for a groin strain this past April. Nothing serious or chronic. Muscle pulls happen.

Miller’s only career arm injury is a bout with elbow inflammation in Spring Training 2012. He’s been on the DL five times in his career: 19 days for a hamstring strain in 2007, 49 days for patellar tendinitis in his right knee in 2008, 25 days for an oblique strain in 2009, 41 days for another hamstring strain in 2012, and 116 days for a Lisfranc injury in his left foot in 2013. The Lisfranc injury required season-ending surgery that forced him to miss the 2013 postseason.

Both guys have dealt with their fair share of pulls and grabs over the years, but, most importantly, neither has had any serious arm trouble. Miller has the more durable looking frame — he’s listed at 6-foot-7 and 210 lbs. while Robertson is only 5-foot-11 and 195 lbs. — yet his Lisfranc injury is by far the most serious injury between the two simply because he needed surgery, though he showed no ill effects in 2014 whatsoever. By reliever standards, these guys are pretty healthy. No major red flags at all.

Contract Estimates

Alright, so how much money are these guys going to end up getting when it’s all said and done? Based on what we heard yesterday, it seems inevitable both will get four years. Here is a roundup of estimates:

To be fair, the FanGraphs and Bowden predictions came weeks ago, before the market blew up and reports surfaced indicating Robertson and Miller were likely to get four years each. The AAV is the more important number there and I am pretty much in agreement with the FanGraphs crowd and Bowden. Using the average AAV spread across four years, we get $46.8M for Robertson and $34M for Miller. That seems reasonable to me.

The Yankees did make Robertson the qualifying offer, which he rejected. So if he were to sign with another team, New York would receive a supplemental first round pick in next June’s draft. They would not gain a pick for signing Miller (duh) nor do they have to forfeit anything for signing either Miller or Robertson. The only draft pick to consider is the one the Yankees would get is Robertson left. I don’t think free agent decisions should hinge on draft pick compensation, not when you’re talking about elite players at their position, but it could serve as a tiebreaker of sorts.

Wrapping Up

So, all of those words and tables and graphs tell us both Robertson and Miller are really freaking good. Picking between them is ultimately a matter of preference. They’re the same age and they’re both going to end up with four-year contracts. Do you prefer the big lefty with the much shorter track record of being elite on a slightly lower annual salary, or the short righty with a nice long track record at a higher salary? There’s a reasonable argument to be made either way. Let’s vote.