Superman vs. Dragonball Z Goku
Ok both heroes know that if the other one loses that their universes and everyone the know/love in them get destroyed. Superman is in current form not Pre-Crisis or Prime and Goku is in his top from from Dragonball Z which is SS3. Battle takes place on a planet just like Earth but no people. So Earth / Outer Space / everything is open. No special items like magic beans or anything is allowed. Who would walk away?