It's really hard to say. Goku has the ability to keep getting stronger through intense battles and transformations. However, Saitama has the power to defeat any opponent with just one punch. If we consider Goku's Super Saiyan Blue form, he has an incredibly high power level. But Saitama's strength has no known limits yet. It could go either way depending on the circumstances of the fight, like if Goku has time to power up or if Saitama can land his punch first.
In my opinion, it's highly unlikely. Goku has mastered multiple forms and techniques that give him a wide range of powers. Saitama's one-punch style might not be effective against Goku's diverse skills and battle experience.
Saitama would win. He has shown incredible strength with just one punch. His power seems limitless, and in a fanfiction scenario, his simplicity and raw power would likely overpower Jiren's more complex abilities.
Well, if we consider Goku's experience in fighting different types of powerful enemies across the universe, he might have an edge in terms of strategy. However, Saitama's raw power is seemingly limitless. In a fanfiction fight, it could depend on the situation. If the fight takes place in a place where Goku can draw energy from the surroundings easily, like a planet with a lot of ki, he might be able to keep up with Saitama. But if it's a straightforward brawl, Saitama's one - punch could potentially end it all.
I don't think there's a clear winner. Both Manga Goku and Manga Saitama have unique and powerful abilities. It could come down to strategy, luck, or even the author's imagination!
In a 'Goku vs Beerus' fanfiction, it's really hard to say who would win. It could depend on how the author wants to write it. If the author wants to show Goku's growth, Goku might win through some new transformation or power - up. But Beerus is a powerful God of Destruction, so he also has a great chance of winning.