Skaggs is the pick here. We are talking about a pitcher who is blessed with both considerable upside and polish. Don't let his underwhelming performance in six starts following his promotion to the big leagues (5.83 ERA, 6 homers allowed in 29 1/3 innings). He has the upside of a No. 2 starter (think Madison Bumgarner).
This is nothing against Eaton, who is a high-energy player who could see considerable playing time the Arizona outfield in 2013. He's a useful speed guy with 10-homer ability, but his ceiling is far from that of Skaggs.
Miley is a bona-fide MLB hurler, but I expect his numbers to see some serious regression in 2013. He doesn't strike out a ton of batters, and I'd be really surprised if he's able to match his BB/9 of 1.71 from a year ago. Ultimately, he's a replaceable fantasy pitcher.