Let me guess, your answer is Goku?
Honestly, I do not have an answer. It always perplexed me.
It's pretty shaky depending wherever you want to go. I'd honestly go with anything pre-Super if you want baldy to have a legitimate shot.
Saitama's strongest statement is from ONE himself saying he can just bop the planet out if he wanted to, but we've never him do anything beyond that, and we can't just assume baseless things we don't have evidence for, so as of now he's just sitting at a planetary level. People generally believe Goku's planetary strength either starts by when he first pops that SSJ against Frieza or, at the very latest, against Kid Buu in the end of the penultimate saga of Z. The whole thing differs because of varying factors.
1. In my own little mind space, even if first form Frieza could blow up a planet, it doesn't exactly translate to his durability since its not his raw strength that's exerted. Final form 100% Frieza is implied that he would have probably survived the explosion of Namek if he didn't yknow
die, and since him and the Goku slapped each other silly that's how some people got the powerscaling from.
2. At this point in the Cell Saga a lot of people just like saying they're gonna blow up the Earth, Cell tried doing it twice. Gohan's the one that popped Cell, and was obviously stronger than Goku at the time, so it made sense why people were still skeptical.
3. Buu literally just bops the planet in the next saga, if you can't take that you got some issues my dude.
Next thing to worry about is speed and reaction timing. Saitama had this whole fight with [jesus christ that's a long name] who kept bragging about this Relativistic speed and Saitama lolnopes him as per usual, but Goku's speed is even iffier to determine because of a magical thing called
animeonlies and much of the original anime being filler or completely different moments with long time periods to make speed-related things a lot more impressive than they actually are. I like to refer to the manga for a lot of these things, and when it comes down to speed it ends up being at a whole whopping "i dont ****ing know". Does it mean he's faster? I don't know. Does it mean he's slower? I don't know. It's just unknown, and (at least for me) I can't determine that based off of the original source material. At the very least he's faster than the human eye, which is way slower than Relativistic speeds. I have no idea where to get speed in Super either, and people toss around MFTL like it's no tomorrow and that's from a calc some guy did about Whis. Is it correct? I don't know, it uses the observable universe as a base and people like to whine that the actual universe of Dragon Ball is tiny, so since nobody can find a middleman I'm still keepint it at unknown.
Final thing is to consider is hax or super-crazy abilities. Saitama only has Mr. Incredible: the Shonen-esque abilities. Goku has a lot of shenanigans, a lot of things people forget is the Saiyan gimmick of "you almost die so now you're guaranteed to be even stronger". Depending on the Goku's chosen durability, and he doesn't die, he will get exponentially stronger in pretty much all stats (IIRC power levels, as bull**** as they may be, refer to strength and speed when someone says they're increased) if not just raw strength and durability.
Goku also has a bigger knowledge of martial arts and pressure points, which can actually disable a person if struck in the right way (Saitama is still human, just a really strong one. Basically Krillin but the main protagonist.), while Saitama is just a punch punch and keep punching with raw strength. Lack of knowledge and a right move can pretty much lock him down before he can strike. Goku also has a bigger variety of techniques (of which he has some that Saitama already does himself) through flight and ki. This also gives him a range advantage if you equalize their speed.
tl;dr Saitama could pull it off before Super happens depending on what you believe, I'm just giving my stance for all beliefs.
I hope Saitama likes life insurance lol he ****ing dead