I'm a ceiling guy not a proximity guy. So I'm going with Hamilton, who made a jump in levels yet still took his game to a way higher level. Top Prospect in Pioneer League says something.
With me, Grandal's upside is essentially to be what Mesoraco is right now but who happens to switch hit. That is why I can't take Grandal over Mesoraco at this point and don't feel its all that close between the two guys.
FTR, I don't see any way that Hamilton isn't a Top 100 prospect when lists start rolling out.