The thing is Saitama doesn't train anymore. He trained for only 3 years and became stupidly strong but stopped because he had no motive to train anymore.

Goku has been training his whole life to the point that he is an training addict. He'll disregard his family and friends to train. He can't stop himself from resisting the urge to get stronger and fight strong opponents.

As of right now, the only reference point we can use is the enemies Saitama and Goku has fought. Goku would easily defeat every villain and hero in OPM. Saitama can maybe defeat Frieza if he lands a punch in Frieza's face. Saitama probably couldn't beat Cell because of his regen abilities. Saitama also probably wouldn't be able to defeat Buu (fat, super or kid).

Saitama is strong but only physically. I think his durability is more of an asset. I don't think he'll be able to defeat some villains from DBZ and DBS, but I also think he can withstand most of their attacks.

If Saitama decides to pick up on training again, he may reach a new level of power and just might get strong enough to take out the stronger DB villains, but he doesn't train anymore.

So as of right now, I don't think Saitama can defeat Goku but I do think he will able to withstand a lot of his attacks. It's just that Saitama doesn't train anymore, so his strength level is going to stay the same while Goku gets continuously stronger.