Whatever weight you think would be most competitive. Ive seen more of Schmeling. Both brilliant strategists, Schmeling probably has more power, Tunney quicker. Both counter punchers. Classic opinion.
For Gene Tunney of the Heeney fight vs Max Schmeling of the Stribling fight, I see this as a tactical battle - a chess match which goes the full 15 with no knockdowns. Schmeling would be trying to land his right cross while Tunney would be trying to avoid it while scoring points of his own. I believe Tunney's footwork and speed would tip the scales in his favor. Tunney by UD.