I would go with Jerebko. I think Gortat would manhandle Zeller. Jerebko probably gets beat too, but at least he gives us spacing. Zeller gives us nothing on offense.
One thing is certain, Horford can't handle both bigs on his own, he needs some kind of help. Stevens doesn't want to mess up his bench rotation, which is understandable, but Olynyk really is the only good(ish) choice here. It seems clear that won't be happening, though.