On just upside I would go:
Pelfrey - college stud
Patton - lefty with amazing stuff, but also still very young
Hirsh - big body and the ability is definitely there, just needs to produce at a high level for another year to prove he's legit
Sowers - MLB ready right now, but I'm not thinking he's going to be a #1 but more of a #2 at the MLB level, but he's a good one
The "safest" choices are Sowers and Pelfrey, but that wasn't the question.