Solomon Grundy is at his strongest
Team 2 wins for the following reasons:
1. Goku should be able to defeat Superboy. Goku has too much power for Superboy to handle, also if Goku has access to all of his forms then it would only worsen the situation for Superboy. There is no indication that Superboy is near Goku's power level and it should be noted that if Goku has access to all of his forms he could simply kill Superboy whilst in his Super Saiyan 3 form by utilizing a a full power Kamehameha Wave at blank point range.
2. Solomon Grundy's strongest incarnation was the one that defeated the Justice League and his strength level was around Superman's level. Considering that Solomon's Grundy's strongest incarnation was around the strength level of Superman then it is quite clear that Silver Age Superman would vastly outclass him in terms of physical strength given his insane strength feats such as moving entire planets with relative ease, pulling 11 planets that were chained together, easily lifting pyramids etc. Silver Age Superman would very easily overpower Solomon Grundy by using physical strength because of the incredibly large gap in the strength department considering SA Superman's ridiculously high strength level.
3. Silver Age Superman is much faster than Solomon Grundy and can easily utilize his speed to evade and dodge all of Solomon Grundy's attacks. Silver Age Superman's speed was so great that he was able to fly to other solar systems, galaxies and even other universes with relative ease. He has on occasions flown sufficiently fast enough to time travel and he flies many times the speed of light with no known limit and at the time he was one of the fastest beings in the universe. And because Solomon Grundy is simply a brick and is very slow he will not be able to land a finger on Superman who could dodge all of his attacks and counter by launching his own attacks.
4. Solomon Grundy is also vastly outclassed in terms of durability. Silver Age Superman was nearly physically indestructible and has flown through the cores of supermassive stars and emerged unharmed, withstood powerful explosions at blank point range (one of these explosions exceeding the power of even a supernova) and it should be noted that Superman performed all of these durability feats without sustaining any physical damage so it is quite clear that Solomon Grundy's attacks will not harm Superman in the least given that this is Superman's most powerful incarnation.
5. Silver Age Superman had insane abilities such as his "Super Sneeze" which has shown him destroying an entire solar system with a single sneeze. Quite ridiculous but strangely impressive nonetheless.
6. Silver Age Superman is virtually tireless and inexhaustible and his body has never been shown to produce any fatigue toxins and it is quite clear that he possesses far superior stamina than Solomon Grundy considering that Solomon Grundy's body does engage in the production of fatigue poisons tiring him in the process.
7. Solomon Grundy is quite stupid and it should be noted that Silver Age Superman is superhumanly intelligent being a super-genius. SA Superman thinks at superhuman speed as he can read information directly from machines etc.
8. SA Superman's heat vision is extremely hot. Regular Superman's heat vision is stated and has been proven to be hotter than the Sun and given the fact that SA Superman's powers are far greater than Regular Superman by ridiculous measures then it can be assumed that SA Superman's heat vision is vastly hotter than the Sun and by proper usage of his heat vision he could potentially harm and seriously injure Solomon Grundy.
9. Silver Age Superman could kill or knock Solomon Grundy unconscious with relative ease and minimal effort however he could also BFR (Battle Field Removal) him I.E he could toss him to outer space etc.
10. SA Superman has a very big advantage: flight. SA Superman could simply remain airborne and launch his long ranged attacks at Solomon Grundy. SA Superman could combine his flight and speed to easily dodge Solomon Grundy's attacks. SA Superman can also tire Solomon Grundy with his speed and when Solomon Grundy is exhausted and open (off guard) he could very easily defeat him with a single blow.
11. Solomon Grundy is clumsy and because of his thick muscular body he does not have good agility while SA Superman possesses far greater bodily coordination, balance and agility that surpasses that of Grundy's by leaps and bounds.
12. Goku and Superboy are well matched in terms of speed considering that both of them can fly at supersonic speed (the speed of sound) however while using Instant Transmission Goku moves dematerializes as a mass of light and moves at the speed of light which is roughly 186,000 miles per second (299,792,458 meters per second). Goku has the speed advantage.
13. In terms of power Goku has the advantage. Goku's energy manipulation is extremely great and he has complete mastery over the usage of ki and well powered Kamehameha could potentially bring Superboy to his knees. One of Superboy's greatest feats of durability is withstanding a nuclear explosions however Goku's power is sufficient to destroy several planets within perimeter as during the Saiyan Saga, Vegeta is already able to destroy entire planets and because currently Goku has far eclipsed the power Vegeta had back then it is safe to assume that Goku's current power allows him to destroy an entire solar system.
14. Goku's martial arts skill will grant him a great advantage during his battle against Superboy and with a good combination of his physical strength and skill he can knock Superboy unconscious.
15. Goku can channel vast amounts of ki energy through his body to augment, increase or enhance his physical power and by doing so he can increase his physical strength and speed beyond his normal levels.
16. If SA Superman were to fight Superboy he would effortlessly defeat him however if Goku fought Solomon Grundy he would lose if he engaged him in physical and close combat however if he maintains his distance then he could quite possibly exploit Solomon Grundy's stupidity and slowness. Goku is also a tactical and strategic genius whilst in battle and this would only increase his and SA Superman's chances of winning this battle.