Hard to say. I like Schmeling's fast right hand over the left which was Tunney's main weapon. I'll go with Schmeling.
My hunch is that the timing would have favored Tunney. Schmeling quickly became a big draw when he landed on American soil, and it is easy to imagine a Tunney who had not retired, seeing this as being the big money fight that he had been hoping woudl turn up. You woudl likely see a prime Tunney, fighting a very good version of Schmeling, albeit one who was still on a learning curve.
When I see Schmeling I see Dempsey with less power but a little more of everything else. This would be a good fight.
People need to stop calling Larry Holmes the most under-rated HW champ & take another look at Tunney, & what he did. He’s a class above Schmeling. He won’t be walking into Schmeling’s counters & his iron jaw render him invulnerable to a Schmeling KO.