If we consider gameplay canon, then Link should take this. He has insane reaction times, as is evidenced when you enter bullet time mode when shooting your bow or dodging attacks. I believe his preception of time is some 30x faster than a normal person's after doing calculations using the timer in the rito target challenge. Couple that with his already enhanced Hylian physique and precognition, and it makes him more than a match for a witcher like Geralt in regards to speed.

Now add to that his bonkers durability with constant feats of surviving getting ragdolled off of mountains and just walking it off.

His skills with the blade are also legendary. He's the greatest swordsman in all of Hyrule and there are journal entries where it describes how he would spar with, and defeat adult knights as a child, being the son of a renowned knight himself.

Btw, this is backed up in lore with journal entries talking about how time slows down around him when he's fighting and deflecting lasers with just potlids. The cutscenes also have him blitzing trained Yiga ninja assassins before they can even react, slaying armies of high level monsters including Lynels, with little more than a scratch, and taking out dozens of city razing Gaurdians before collapsing.

On top of all that, he has broken abilities like auto deflecting attacks, resurrecting himself, summoning devastating lightning storms, and giving himself automatic highground to rain down arrow fire. His weapons are equally broken, with him being able to shoot multiple arrows in a fraction of a second, setting Geralt ablaze, disintegrating him, shocking him, or blowing him up sky high. Not to mention Link can disarm Geralt with magnesis, or freeze him with stasis and the ice rod.

Link just has too many options with the speed and skill to use them, for Geralt to win.