It's a mixture of a bad bullpen and a few struggling starters for the Chicago White Sox six-man rotation that this question must be brought up.
Unfortunately, there's no real positive answer to the question.
If you go based on history, Phil Humber would be the odd man out, seeing as he had only pitched 41.1 innings coming into this season, but he's arguably been the best White Sox pitcher, sporting a 3.06 ERA and a 0.97 WHIP in 67.2 innings pitched.
If you go based on health, Jake Peavy would be the odd man out, coming off of shoulder surgery, but he's sporting a 3.24 ERA and a 0.88 WHIP in 25 innings.
If you go based on numbers, John Danks would be the odd man out, sporting a 5.25 ERA and a 1.57 WHIP in 70.1 innings pitched and apparently caring more about idiotic unwritten rules for pitchers to whine about than pitching.
Danks, however, is supposedly your ace of the future.
As long as Mark Buehrle stays below a 4.00 ERA (he's at 3.91), he'll always be in the White Sox starting rotation, so that's out the window.
Gavin Floyd is safe as well with a 3.69 ERA and a 1.09 WHIP in 68.1 innings pitched.
Which brings us to the some times dominant, but mostly inconsistent Edwin Jackson.
With a 4.63 ERA, a 1.53 WHIP, having given up 79 hits and walked 25 in 68 innings, Jackson fits the numbers requirement. History-wise, Jackson has never been consistent, finishing below a 4.00 ERA once in his career, only to jump nearly a full run in his ERA the very next season. His earned runs in his 11 starts this season in order are two, one, three, four, seven, six, one, zero, four, one, six.
Jackson is showing why he's on his fifth team in the last six years.
Unfortunately, the White Sox are paying him $8.35 million, which is a bit hefty to be paying a long reliever. With Chris Sale (5.31 ERA), Matt Thornton (5.60 ERA), Chris Sale (5.31 ERA), Will Ohman (5.93 ERA) and Tony Pena (6.20 ERA) making up four of the spots in the bullpen, the White Sox may not have a choice.
On the other side of the argument is the thinking that the starting pitching may have been solid of late due in part to the competition this idea of being sent to the bullpen is making.
It would seem as though management is waiting for an answer to be given to them, whether in the form of an injury or Humber falling off the wagon, but no easy answer is coming to fruition.
If Jackson continues to be inconsistent, the answer may be clear for the White Sox.
John Danks shouldn't get too comfortable either. As long as the White Sox bullpen is seemingly leftyless with Thornton forgetting how to pitch, Ohman remembering how not to pitch and Sale in a sophomore slump and Danks pitching awful, like a kid being sent to the timeout chair, a march to the bullpen could be in order.