Probably Embiid.
As injury prone as Embiid is, he is in the air and moves around about half as much as Zion. As big as Zion is and as physical and athletic as he plays the game, I think he's a ticking time bomb for a catastrophic knee or ankle injury.
Plus, Embiid is already elite, and has been for a year or two now. None of the other guys are even close to that level yet.