Johan. Along with Halladay, the track record is as proven as they come. The offense is the most potent of the others listed, and the 8th & 9th guys don't get any better.
Greinke was my vote but almost went with Santana. Santana will be great the rest of the year, but you can't argue Greinke's stats. He is unbelieveable right now.
Greinke has been unbelievable no doubt, I'm just not ready to put him in the same sentence as Santana, yet at least. I wanna see a full season at least of dominance.