I’ll give my two cents and say that the Six Paths of Pain have the advantage.
Garou has much greater fighting experience and his fighting styles like his Water Stream Rock Smashing Fist or the Cross Fang Dragon Slayer Fist are far beyond what Pain can manage. Garou’s reactive evolution could also allow him to overpower the Pains, not to mention with speed unequalized, he has a speed advantage.
However, the Six Paths of Pain have a shared field of view that would allow them to more accurately evade Garou’s attacks. Their numbers also give them an advantage: though Garou has fought against numbers, the heroes he fought were much weaker than him, some of whom he could take out in a single hit, and they didn’t have as good teamwork. These opponents are almost just as strong as him and can perform coordinated attacks, which Garou hasn’t had to deal with.
Each of the Pains possess each of their unique Justus which would give Garou some trouble. For one, the Animal Path could summon a variety of different creatures that could all pounce on him, and this Garou’s fighting style still can’t deal with animal opponents. The Asura Path’s mechanized body could also pose a problem, since he doesn’t have too much experience fighting mechanized opponents and has only fought Genos. However, the Deva Path would pose the biggest problem: his Shinra Tensei could damage Sage Mode Naruto and Jiraiya. If Garou gets hit with it, then he very likely gets killed, if not seriously injured. If by some chance that didn’t kill him, then Pain could just finish him off with the Human Path and suck out his soul. Even during the battle, Pain could try and pin Garou down to suck his soul out. I think Garou had higher LS, it’s still in the same Class G, and if multiple Pains work to pin him down, it’d be enough to keep him in place. Pain pinned Naruto down with one of the Pains, so it’s in-character of him, not to mention he can use the Chakra Rods to keep Garou in-place.
Pain’s cautious in-battle, so when he sees Garou rapidly evolving, he’ll try and finish him off with the Chibaku Tensei, which will definitely kill Garou.
Overall, Garou could potentially destroy the bodies of the Pains and evolve quickly enough to deal with them, but it just doesn’t seem likely with all of Pain’s other advantages.
