The idea of having a rebooted universe rebooted in the same film is insane. For this reason alone, it must be TOS Spock.
Exactly. The producers and writers intended for Spock to come from the Prime Universe. Period. There would be no reason to have him in the film otherwise. Any other fanon ideas about an alternate universe is just someone's opinion, based on very shaky evidence. Saying 'things don't look the same as in the Prime Universe" is not a valid excuse. It can be argued that the entire series of ENTERPRISE doesn't fit within what's known about the Prime Universe in the 22nd century, but it was still what the creators intended, and there's no way around that (and believe me, nothing would make me happier than to learn that ENT was not part of the accepted canon).
Someone else posted a thread essentially saying the same thing you are, but using Nero and his crew as the subject. His hypothesis? Because they didn't have hair, they weren't Romulans from the Prime Universe (never minding that both Nero's wife and another female crew member did
have hair, it's quite a flimsy argument).