Goku vs. Superman is a hypothetical battle that has been argued by fans ever since Goku reached Super Saiyan status back in the early 2000’s, putting him on par with Superman. Being that these characters and their stories are ongoing, the circumstances of their battle change with each new arc and reboot. Recently, Goku has obtained the power of 'Super Saiyan God', and Superman unleashed a 'Super Flare' once his heat vision had reached its limit. So the question arises again. Who would win?
Goku's a hero whose strength is constantly growing. As a Saiyan, he possesses the ability to increase his powers dramatically every-time he comes close to death, or in some cases, dies. Many have argued that Goku could take Superman out with a Spirit Bomb that harnesses energy from not only the planet but from around the universe. However, this theory's flawed. For one, Superman's a good guy. Those who're pure of heart cannot be harmed by the Spirit Bomb. And two, Superman has survived a supernova, and essentially gets his energy from stars, which's what a Spirit Bomb that harnesses energy from the universe would consist of.
One way that Goku could stand against Superman is by using his new-found ability, Super Saiyan God (obviously, Toriyama is running out of titles). This allows Goku to retain the once temporary powers of Super Saiyan God. Going toe-to-toe with Superman (whose strength knows no bounds) would prove destructive for wherever they do battle. As protectors and allies of Earth, they'd most likely take their battle to a remote planet using Goku’s Instant Transmission technique. Though Goku has Superman beat when it comes to speed, Superman blows Goku away in Strength. Superman once bench-pressed the entire weight of Earth for five days straight. If Superman could land one full-power blow, Goku would literally be torn to pieces under its shear force, along with whatever unfortunate planet they chose to spar on.
As a DBZ fan, I absolutely hate to admit it, but Superman would win. Goku is faster and has amazing strength, but unless he went around obliterating every star feeding energy into Superman, Goku would run out of steam well-before Superman. Once that happened, Superman would gain the upper-hand. Knowing Goku, he would stubbornly continue to fight with whatever energy he had left, assuming there was no one around to lend him their strength or feed him Senzu Beans. Superman would then use his Super Flare to completely put Goku out of commission. Otherwise, he would risk a powerful comeback from Goku whose strength grows with every beat down. Thus, their battle would reach an end.