Uh, I think he's the easist to let go. He has such a long way to go before making the bigs and, in all honesty, looks more like a reliever than a starter.
Rendon would be the toughest. That bat would be fantastic in front of Zimmerman and Harper
Rendon has been injury prone since we got him. I think Upton would deliver as much offensively as Rendon potentially could.
The only problem that leaves us is at first base next year. I would be fine for keeping them too but if this offer was on the table, I'd do it.