Silver Age Superman wins for the following reasons:
1. Silver Age Superman greatly outclasses all of the fighters: Goku, Solomon Grundy and Superboy Prime in physical strength to the point of ridiculousness. Silver Age Superman has shown a feat of strength that completely overshadows the strength feats of the other fighters, Solomon Grundy's greatest strength feat was defeating the entire Justice League, Superboy Prime's was moving entire planets and Goku's is ripping out a street intersection by using all of his physical strength whilst in his Super Saiyan 4 form. SA Superman's greatest strength feat was pulling 11 chained planets with minimal effort and ease. SA Superman's physical strength vastly outclasses that of any other fighter in this battle combined. His other strength feats include easily overpowering the forces of black holes, lifting large pyramids with extreme ease, tossing large mountains etc. his strength is ridiculously high and too much for his opponents and he will very well overwhelm them.
2. SA Superman is also much faster than every other fighter in this battle. He has flown so fast to the extent of time travel, flown over 500x the speed of light with no effort whatsoever and is functionally known as one of the fastest beings in the universe. SA Superman's speed has been sufficient to fly to distant solar systems, galaxies and entire universes with ease and he is able to vibrate his molecules to move through solid mass. None of the fighters in this battle has displayed such speed as Goku while using IT (Instant Transmission) is at his fastest and moves at light speed, Solomon Grundy is extremely slow and a grounded brick and is not even faster than a train, Superboy Prime is the fastest opponent SA Superman will have to deal with however Superboy Prime was not fast enough to avoid an attack of two Flashes/Speedsters while SA Superman is much faster than any Flash. SA Superman could simply dodge and evade all of the attacks launched at him.
3. SA Superman is too durable for any of his opponents to seriously harm him. SA Superman has survived entire supernova explosions at blank point range and simply shrugged it off sustaining no physical damage and remained conscious, he has flown through the cores of supermassive stars and he has never been shown to be physically harmed, a characteristic than none of his opponents have shown and he is quite possibly invulnerable to physical damage. SA Superman's durability is due to his super-dense molecular structure. His opponent's durability feats include: Goku's greatest durability feat is withstanding the temperature of the Sun or slightly higher at the hands of Nuova Shenron, Superboy Prime has flown through the cores of stars emerging unharmed (a feat also performed by SA Superman himself) and Solomon Grundy's was withstanding attacks from the Justice League, SA Superman outclasses all of those feats as he easily withstood a supernova explosion at blank point range without fazing or sustaining physical damage.
4. Silver Age Superman has far too much power to be handled by any of his opponents. SA Superman's power is so ridiculously high that he has on one occasion destroyed a solar system with a single sneeze (by accident) and with that shown and also being an accident one can assume that his full power would be of truly monstrous and terrifying proportions.
5. SA Superman has had the highest superhuman agility, bodily coordination and balance of all involved in this battle. SA Superman has great fighting agility and is able to perform complicated acrobatic maneuvers.
6. All other fighters in this battle except SA Superman are able to tire. SA Superman's body does not produce any fatigue toxins thus rendering him tireless and inexhaustible. Superboy Prime can engage in intense physical activity for a certain period of time before his body produces fatigue poisons that impale his blood circulation tiring him in the process, this goes for Goku and Solomon Grundy who have even lower stamina than Superboy Prime.
7. SA Superman does not require to breathe, eat or sleep and the same goes for Superboy Prime. SA Superman could simply fly to space, fight and defeat Superboy Prime there and return to Earth to defeat the remaining opponents who cannot survive in space without any form of sustenance and support.
8. Like all of the fighters in this battle except for Solomon Grundy, SA Superman possesses the power of flight. Goku is not a serious threat to SA Superman no matter what form he takes, the same goes for all of the incarnations of Solomon Grundy and Superboy Prime is only a minimal threat. SA Superman could simply fight both Superboy Prime and Goku whilst airborne leaving Solomon Grundy who is unable to fly, grounded and temporarily out of the battle. SA Superman could proceed to defeat both Superboy Prime and Goku and return to defeat Solomon Grundy who is a grounded brick.
9. SA Superman can easily BFR (Battle Field Removal) Solomon Grundy because of his superior physical power I.E he could toss him into space or into the scorching Sun. SA Superman could also overpower Goku and force him into space where Goku would die because of lack of oxygen which he requires to survive and the only times Saiyans have shown the ability to survive in space were in non-cannon (not in direct continuity to the original series A.K.A not correct) movies and in the manga it is stated several times that Saiyans cannot survive in space. Superboy Prime could be defeated by SA Superman fairly easily because of possessing superior power.
10. Regular Superman's heat vision is already hotter than the Sun and SA Superman's powers are freakishly much higher than regular Superman's powers ergo his heat vision must be many times hotter than the Sun and he could potentially incinerate Goku with his heat vision by widening it covering Goku's entire body burning him to death considering that there is no evidence that Goku could survive that sort of temperature (many times hotter than the entire Sun) or he could seriously harm or injure Goku.
11. Overall SA Superman wins because of possessing far superior power than his opponents even combined for obvious reasons and reasons stated above in the previous posts.