why? Superman can
destroy planets with his fist. he is tough enough to withstand
being crushed between two planets or
the destruction of a solar/star system.
so, how does Superman not get beaten by Goku?
for one, Goku can't hurt him. Goku's Kamehameha can destroy planets, Superman can tank planet busters.
two, unlike Superman who can tank planet busters, Goku cannot. he was killed when Cell 2 self-destructed and one of his most powerful villains, Kid Buu, was destroyed when he blew the Earth up(he lived thanks to his magical regeneration). Kid Buu and Super Saiyajin 3 Goku are about even(Buu may slightly be stronger). so Goku can be killed by a planet buster, can Superman busts planets? yes, he surely can.
but then, there is the speed. let's take care of that.
using Cho Gohan/Mystic as an example. Cho Gohan is the most powerful non-fusioned character in DBZ, he was easily beating the hell out of Buu(before he absorbed Gotenks). but before that happened, he had to get to Buu and his friends first. and despite being very powerful it still took him a while to reach his friends. speed in DBZ is dependent on their Ki. this was confirmed in the Android saga when Goku told Gohan to slow down otherwise he'll run out of Ki. so, the more power the more speed they have. Cho Gohan being the most powerful non-fusion character is also the fastest in DBZ, and he's slower than Superman.
because Superman can fly from
Earth to one of Saturn's moons in 4 minutes.
other powers and techniques by Goku like his teleportation will only work once against Superman who has experience against teleporters. Solar Flare is useless since Superman dives into stars and suns, he can never be blinded by light. Energy Spirit Ball/Genki Dama only works on the wicked, which Superman isn't. and Superman
knows how to fight very well, he's not just a brawler.
conclusion, Superman.