It's a hard choice because Greinke has been consistent all year long but Jake has been way better than everyone since the all star break. There's also the fact that he's had to pitch against the Cardinals and Pirates while Greinke's opponents haven't been as good. Hopefully the writers do a little research instead of just voting based off of ERA. That said, I couldn't be mad if they have it to Greinke because he's had an epic year as well. Either way someone deserving of the award isn't going to get it.
Two weeks ago (and the entire time before that), it was Greinke. He had an ERA about a third of a run better than Jake. At this point, Jake is only .14 lower (1.68 to .1.82) That's nothing.
On the other hand, Jake has more wins (21 to 18), more innings (223 to 214.2), more shutouts (3 to 0), more complete games (4 to 1), a very similar WHIP (.852 to .879), the same number of hits per nine innings (6.0...I think Jake leads by hundredths), more strikeouts (229 to 192), etc.
The main argument for Greinke is ERA, but that gap has narrowed. They've both had historically good years. It will be a shame that one of them gets second.
ETA: Jake has also had one of the best stretches since the dead ball era since the All Star break. Truly dominant.
