I voted Stephenson based on his stuff and potential. He's the prospect with the greatest ace potential since Homer Bailey, and that's saying something. His high school numbers were unreal as well.
Boxberger and Corcino are nice, but lets not forget how badly Boxberger struggled in AA at the end of last season. He rebounded quite nicely, but it's a reminder that he's still far from a sure thing. Corcino's season was nice as well, but he was playing in a pitcher's league and had worse stats than Josh Smith. I need to see more out of him before I put him this high.