IMO the two catchers are the Reds' top prospects right now.
I have no doubt that any team offering a high end starting pitcher will insist on Mesoraco in the trade. I don't believe for a minute that a high end pitcher is coming for Alonso, Volquez, Travis Wood as the featured player. They will all want Mes.
The Reds could try to construct a package offering Grandal. That may bring a lesser pitcher. Or it may require the Reds giving up more talent (Stubbs, perhaps).
So the question is presented whether the Reds should trade Mes if necessary to land a high end pitcher.
Or, should they trade Grandal for perhaps a somewhat lesser pitcher. Or Grandal may require giving up someone like Stubbs.
Or, is it premature to trade either. Hold on to both of them and see who pans out.
My view is that I wouldn't trade Mes, and I would only trade Grandal for a high end pitcher. I think these two guys are very valuable and (through a position change) both could be regulars for the Reds soon.
But I realize that holding on to these prospects could eliminate the big trade.