Patrick Corbin seems to be in the driver's seat to win the final spot in the Diamondbacks' rotation. He's been impressive this spring, going 3-0 with a 3.66 ERA in six outings (four starts. Honestly, though, I've been most impressed with the fact he has struck out 19 batters in 19 2/3 innings.
Last season, Corbin struck out 7.2 batters per nine innings in 22 outings (17 starts), but he definitely has room to grow in that area because he struck out 8.4 batters per nine innings in the minors.
It's not overly surprising to see Corbin the front-runner to win a spot in the Diamondbacks' rotation. While Tyler Skaggs and Randall Delgado might have more long-term upside, Corbin went 31-16 with a 3.78 ERA and 1.27 WHIP in 430 2/3 minor-league innings, so it's not like he was a slouch in the minors. It's just that his upside might be as a mid-rotation arm in the majors at best.
I'd leave Corbin for NL-only and deeper mixed leagues on Draft Day.