DISCLAIMER: I do not own Dragon Ball Z or Marvel Comics.
Goku hovered in the sky, casually reflecting on his time on Earth. He felt he had achieved his fair share, though he wished he could keep the ones he cared for safe. He had always wanted nothing more than safety for those of pure heart. Suddenly, he looked down in horror as he heard the familiar voice of Piccolo in his head. Piccolo was in trouble. Goku used Instant Transmission, reaching Piccolo, as the name suggested, in an instant.
Piccolo lay on the ground, horribly bruised and bleeding. A green giant stood over him, snarling. As the monster was about to finish Piccolo off, Goku flew forward and picked it up, flying into the air with it before blowing it away with a Ki blast. The creature roared with rage, charging back at Goku.
"Hulk smash!"
Goku sidestepped a series of attacks from the creature, Hulk, Goku guessed he was called. Goku was far faster than Hulk, and was dodging his attacks with time to spare, while landing attacks of his own at the same time, but there was no doubt in his mind that Hulk was stronger. Goku could sense no power level, but he could sense a great deal of strength. Goku's instincts told him that if Hulk was able to hit him, he would be lucky if he wasn't killed.
Goku then jumped away, quickly powering up to Super Saiyan. Hulk charged after him, but Goku jumped past the charging green monster, firing a blast into its back, though to no effect other than a grunt from Hulk. Hulk picked up a large chunk of stone, ripping it straight out of the ground and flinging it at Goku. Goku shattered the rock with a Ki blast, before diving into the air to avoid the charging Hulk.
From the air, Goku fired multiple Ki blasts, but still to no effect beyond making Hulk angrier, which seemed to make him stronger. Hulk then jumped into the air, launching himself straight at Goku. Goku would have been caught off guard except that he had expected this approach. Goku flew to the side, avoiding the airborne Hulk, before firing a Ki blast into him, launching the green monster away. Goku watched as Hulk crashed through mountains, shattering them like glass. Hulk then jumped back into the air, flinging a large shard of stone at Goku, who shattered it with a Ki blast before flying up higher and beginning to charge his Kamehameha. Hulk landed below Goku, launching himself up at him. Goku used Instant Transmission just as Hulk reached him, teleporting back to the ground and firing his Kamehameha at the still airborne Hulk, blasting him straight up into the sky.
As Goku breathed in a deep breath, Hulk reached low orbit, before falling back towards the ground. Goku looked up to see the raging Hulk falling back towards the ground, and quickly powered up to Super Saiyan 2. Goku then used Instant Transmission to avoid the falling Hulk's destructive landing. Goku fired a Ki blast at Hulk, but even as a Super Saiyan 2, his attacks did little more than infuriate the already raging Hulk.
As Hulk picked up a huge chunk of stone from the ground and charged, Goku fired a blast through the stone, shattering it, before using Instant Transmission just before the Hulk collided with him. Goku reappeared in the air, and quickly powered up to Super Saiyan 3. Hulk then jumped into the air after him, only just missing Goku, who flew to the side and fired a Ki blast into the Hulk's head from the side.
The blast launched the Hulk through several mountains, but ultimately, the Hulk was unharmed, and had gotten angrier. Hulk charged, while Goku quickly charged up a Kamehameha, firing it straight into the charging Hulk, launching the monster back, causing him to skid across the stone ground. Again, Hulk was unharmed, and was really only made angrier.
As Hulk charged once more, still as fresh as he had been at the start of the fight, if not fresher, Goku quickly powered up to Super Saiyan 4, reaching his full power. Alone, he could not achieve Super Saiyan God, nor could he fuse with anyone. Goku charged at Hulk, diving to the side at the last second and firing a Ki blast at the Hulk, launching him through the air again.
Hulk reappeared once again, still showing no sign of injury. Goku charged again, this time picking Hulk up off the ground and flying into the sky with him, punching him as he went. The Hulk showed no great pain from the hits Goku was delivering, but any hits he threw at Goku were easily avoided by the Saiyan due to the Hulk's far inferior speed. Goku then released Hulk, flying back and charging with his devastating Dragon Fist technique.
Goku's fist slammed into the Hulk, boring straight into the monster's chest. A golden dragon of Ki was generated by the punch, and wrapped around Hulk. Hulk's roars became increasingly angrier as the Ki dragon of the Dragon Fist dealt him horrific damage. Finally, the Ki dragon faded, and the Hulk fell back to the ground, leaving a huge crater. Goku flew down in front of the Hulk, who was already standing back up again.
Goku's mind was racing. "This can't be. The Dragon Fist and a series of blasts… while in Super Saiyan 4! How can he still move? And how can he be even stronger now than he was at the start?"
Hulk charged at Goku once more, now moving faster than before. Goku was still much faster, and took to the air, avoiding the charge. Hulk jumped up into the air, swinging his hand at Goku. Goku avoided his strike, firing a Ki beam into the Hulk's side and launching him several miles away.
Hulk returned, jumping up after Goku once more. Goku avoided the strike, flying higher into the sky, just below the atmosphere. Hulk jumped up again, still reaching Goku, who barely avoided him. Goku now had a plan. He had observed the Hulk's erratic attacks, and thought he knew what to do. Goku fired a blast into the Hulk as the Hulk fell, launching him back down to the ground. Hulk landed heavily on his feet, carving out a ravine upon landing. He then jumped back up, aiming straight for Goku, who was charging a powerful Kamehameha.
As Hulk reached Goku, and the monster's massive green hands were about to close around him and tear him apart, Goku used Instant Transmission to teleport below the Hulk, before firing the Kamehameha into him from below, launching the monster straight through the atmosphere. By a turn of strategy, Goku had also lined himself up so that Hulk was directly between him and the Sun.
Goku's Kamehameha blasted Hulk straight through the atmosphere, straight past Venus and Mercury, and finally into the Sun. The Kamehameha impacted on the star with the green monster stuck on the business end of it. Hulk roared with boundless rage as he penetrated through to the Sun's core, before flying out the other side. Hulk was alive, but on a one way trip to the other end of the galaxy. Millions of miles away, on Earth, Goku released a sigh of relief, returning to his base form. As he surveyed the damage around him, one thought was prominent in his head.
"I wonder what's for dinner?"
Reasons for this outcome:
1. While Hulk is far stronger and more durable than Goku, having survived being launched into stars before, and been stated as having limitless strength, Goku is so much faster and more skilled that Hulk would be lucky to hit him once, though a few direct hits from limitless strength Hulk would be adequate to kill him, regardless of Ki or Super Saiyan states.
2. Though Broly and Cooler are non-canon, and cannot be used as central evidence, it still fits that Goku could fight like that, launching his enemy into the Sun. Hulk can survive in space, but he cannot fly, so he would be incapable of returning immediately after being launched into space. The only way Hulk could return from space is if someone else brings him back, or if he finds a mass in space such as a meteor or a planet that he can use as a platform to jump back.