Heyo! After watching Gurren Lagann, it's become seemingly more apparent that Gurren Laganns strongest form, would be able to be on par, or even beat goku or superman. let's analyze and debate this in the comments below!
Goku grows stronger with every battle, and in recent movies now has a Super Saiyan God form, which has proven to last against the god of death himself. Goku has power to blow away planets, and seems to live a apparently long life, so he has ample time to train and knows many martial arts and powers dealing with Ki. Goku heals fast as well, but by no means has regeneration. He has died multiple times in battle, but never the less is strong.
Superman, many people say he is the strongest hero of all time. From the comics point of view he has carried planets on huge chains, lifted the entire EVERYTHING of all the universe, and has stronger forms as well (i won't get into that, not very aware of those forms), but on a more realistic form that still includes his powers, Superman drives all his power from the Sun, a single star in the milky way that feeds him radiation. Superman is called the man of steel, but is not invulnerable. Speaking hypothetically, superman only feeds off the suns radiation, so a blast with as much power as a sun would most likely obliterate him. Never the less, in comic book form, very op.
Gurren Lagann, a robot used to fight anti spiral energy foes in a galactic war. Although the beginning of Gurren Lagann is weak and makes him seem frail, the end of Gurren Lagann shows that the final form of this robot is able to take, and absorb a blast on level with that of a Big Bang. Gurren Lagann is also the size of many, many solar systems, and although has been beaten up and damaged it can repair itself with spiral energy, or fighting spirit.
Please note that this is a debate on who would win in their strongest form, not under any certain circumstances or with people around that would make them hold back. This is a fight to the death, nothing held back.