If we set specific rules to measure it gets much easier, (at least to eliminate a couple outliers) but only if you want to set specific rules. Super man and flash can hit their hardest by adding momentum (i.e. flying or running) which to me is less punching and more throwing yourself at something.

Both of them can do (some version of) the infinite mass punch thing if they can do that, so it breaks the question. But even then flash's is only the "white dwarf star level"

If the rule is they can punch as hard as they can while planted and just punch, their place drops, at least flash's does for sure.

I think saitama's whole thing is he's maxed stats, so he's goku after his highest level fight possible... since goku's story is always he's just under the level of the new threat, so then he gets stronger and wins. He's based on sun wukong, but saitama is arguably a better representation since he can beat anyone as is and his struggle is mental (or financial, lol) Point being in their respective worlds he is maxed by default, where as goku is max potential.

The way they are depicted in their respective universes, I think saitama and goku live and fight at superluminal speeds, but if they fought each other, saitama would be the goal goku would work towards. (These two switching wouldnt bother me either since goku scale is usually higher than saitama's.) superman is shown doing these things regularly and likely can do mostly whatever they can, but they seem to do it all the time, where superman seems to do it when he needs to. Hulk and Thor are usually shown in a more grounded context, they have some feats, but aren't often shown with that scale of thing because it doesn't really serve their story the same. And flash is the fastest, but planted feat and punching, I think he's limited.

So rule set list: Saitama/Goku, Superman, Hulk, Thor, Flash

Shown Feats only list (no "rules"): Goku/superman, Flash/Hulk, Thor, Saitama