It's hard to say for sure. Naruto, in his godlike state, has incredible power like being able to create and destroy on a large scale. But The Flash, with his ability to move at near - infinite speed and break the laws of physics in his own way, is also extremely powerful. It could be that Naruto is more powerful in terms of raw destructive power, but The Flash has the edge in terms of mobility and reaction time.
It's really hard to say. Naruto with his godlike powers would be extremely powerful. He can do things like create massive Rasengans and has near - unlimited chakra. But Superman in the Justice League also has incredible strength, speed, and heat vision. He can fly at supersonic speeds and is nearly invulnerable. However, if Naruto's godlike form gives him the ability to manipulate time and space like some of the Otsutsuki in his world, he might have an edge over Superman.
It could be Naruto. His godlike form in Naruto already gives him incredible power. If he were to gain quirks on top of that, he would be extremely formidable. His ability to create thousands of clones and his vast chakra reserves combined with a powerful quirk would make him a top - tier character.
However, it might not be just about Naruto or Goku. A new character created through the fusion of Naruto and Goku's powers could potentially be the most powerful. This character would have the best of both worlds - the Saiyan's fighting instincts and raw power along with Naruto's strategic thinking and unique ninja abilities.
I'm sorry, I don't know who the author of this fanfic is. There are so many fanfic writers out there and without more information, it's difficult to determine the author.
The 'godlike' powers could be integrated as an evolution of Naruto's existing chakra powers. Maybe he discovers a new form of chakra that gives him 'godlike' abilities like the ability to create or destroy matter at will. The 'flash' powers could be added to his movement skills, like he can move at super - speed by channeling this new form of chakra.
It could be Naruto in his Nine - Tails Chakra Mode. He has immense power and speed, which would give him an edge in the Smash Bros battles.
It's hard to say for sure, but Naruto could be a very powerful character. His ability to use chakra and his vast array of ninja techniques like the Rasengan and Shadow Clone Jutsu would give him an edge. However, in the RWBY world, characters like Ruby with her Silver - Eyed Warrior powers also have great potential.
However, Jin Kazama from Tekken also has a strong claim. He has the Devil Gene which gives him enhanced abilities. He can transform into a more powerful form and has years of martial arts training. If he could somehow learn to control Naruto's chakra or ninja techniques, he could become extremely powerful. In a Tekken Naruto fanfic, it might depend on how the powers are combined and who has the better strategy in a fight.
In a fanfic, it could really depend on the story's direction. If the story focuses on Boruto's growth and he unlocks the full potential of the Jougan, he could be the most powerful. The Jougan seems to have some mysterious and potentially very strong abilities. But Sarada could also become extremely powerful if she manages to awaken new levels of the Sharingan. Naruto, while powerful, may be surpassed by the younger generation in a story that emphasizes their rapid development.
It's hard to say for sure, but Naruto at his strongest form, like in his Six Paths Sage Mode, would be extremely powerful. He has incredible speed, strength, and the ability to use all kinds of ninjutsu. In the Fate world, he could give a tough fight to many Servants. However, some of the really powerful Servants like Gilgamesh with his vast collection of powerful weapons and his god - like status would also be a strong contender.