Once the postseason nears though, the ranking takes on a whole new importance. Questions arise about the postseason rotation and who will start what game in the ALDS. Max Kellerman used to argue that Game 2 was actually the most pivotal game of a 5 game series because it always swings the series between 1-1 and 2-0, either pulling one team back to even or putting them on the brink of elimination.
Since Kellerman's theory is a bit radical, I think we can safely assume that Joe Girardi is going to attempt to line up his rotation with his best pitcher starting Game 1 and so on. Since only three games are guaranteed, it also matters who the top three pitches are. It's clear that CC Sabathia slots in at the top of the rotation and Joba Chamberlain would be their 4th starter. So the question comes down to Burnett vs. Pettitte for the number two slot.
NoMaas makes the case for Pettitte and it's hard to argue against it. Pettitte has been on a better run recently and his numbers for the season are stronger as well. Both have made 27 starts and you might be surprised to learn that Burnett has pitched only 2 1/3 more innings than Pettitte with each averaging just under 6 1/3 each time out. Pettitte has a better ERA, WHIP, FIP, K/BB, HR/9. Burnett leads in quality starts 18 to 15 (fairly significant) and has struck out more per 9 IP while allowing fewer hits, but has walked one more per 9 (which is how his WHIP is worse).
It's worth noting that on June 20th, their ERAs were almost exactly the same (4.24 and 4.26) but Burnett proceeded to go on a run that saw his drop to 3.53 at one point while Pettitte's rose as high as 4.85. Burnett's great stretch was better than anything Pettitte has done this season and the reality is that upside is always tantalizing in sports.
Burnett has never pitched in the postseason (he was injured with the 2003 Marlins) and Pettitte has thrown 218 1/3 playoff innings to a 3.98 ERA over the course of 25 series.
Moshe at the Yankees Universe introduces another interesting factor: home/road splits. Oddly, although Burnett is the righty of the two, he has better numbers at Yankee Stadium while Pettitte has done his best work on the road, with a roughly 1.3 run difference in ERA in both directions. If the Yanks hang on to win the division, Game 2 will be at home. Jason from Heartland Pinstripes would prefer to give Burnett the start if this turns out to be the case.
It will be interesting to see how heavily Joe Girardi weights September performance into the equation. With about 5 or 6 starts remaining for each, much can change. If the ALDS started five days from now, I'd probably go with Pettitte. If Burnett has a decent September I'd probably choose him. Either way, every start in the postseason is important and the Yanks are lucky to have guys as good as those two jockeying for position.