I forgot this... Sans is capable of sensing and knowing Frisk's Level of Violence, Execution Points, and feelings
when the two meet in the Judgement Hall, which
is listed as clairvoyance and extrasensory perception on Sans' profile, which would spell trouble for Golden Freddy trying to use stealth mastery and maybe even some kinds illusions. Sans should be able to use those abilities to sense a person's hidden presence, although he hasn't been directly shown doing that.
Sans is also capable of dodging while asleep, so I don't think a headache would stop him from acting.
Despite all the discussion of Golden Freddy taking a long while to defeat target using mind hax,
I saw a FNAF 2 clip of Golden Freddy taking less than two seconds to jumpscare the main character, and since Golden Freddy zoomed as only a head, there couldn't have been any physical grabbing.
Golden Freddy did reveal himself for a split second in the flashlight's light beforehand though.
Based on the aforementioned details, I think Sans would come out on top. Sans' clairvoyance, extrasensory perception, and instinctive action, combined with Golden Freddy being willing to toy with his target before moving in for a swift kill, should allow Sans to be more than prepared to hit Golden Freddy upon discovering him. Does that seem right to you?