I dont think strength or toughness would play a factor in this fight
both can withstand and
deal massive physical trauma
Lets use this as an example, in DBZ the characters get tossed around at lets just say for simplicity, any speed up to.... mach 2, which is 680 m/s almost instantly, but lets say it takes 1 second to reach the velocity from the average strike of a newly introduced villain
Lets also say, goku weighs 230 pounds or so
so doing the math, Goku would hit, lets say a mountain, with... 156400 N of force, or 35160 pounds of force(I believe I got it right). superman would have to be able to hit harder than that to deal damage and vice versa
Also, in DBZ, goku could withstand massive explosions of energy, deflect them even, with barely a scratch, but superman could take a supernova level explosion, so Goku wouldn't be able to hurt him either
It'd have to come down to a weakness, and both have them unfortunately
Goku is susceptible to disease and poisons
Superman is susceptible to Kryptonite and radiation
whoever weakens the other first wins imo
Ima go give goku the flu and see what happens.