While it is a fun question, it is not in any way an important one.
The answer is canon is whatever works for you.
canon is TOS, TNG S1-6, DS9, Star Trek movies 1-4, 6, FC, and then this Abrams Trek.
WOw, amazing! Star Trek canon is more or less batting 100% in terms of being at least "good and entertaining"
LOL, I notice glaring absences: TNG S-7, ENT, ST:V, and so many TNG films.
Better question, now: if you understand that, say First Contact
operates within the universe created by Generations
, and you accept the universe of First Contact as canon, does that not make you implicitly accept Generations
as canon also? I mean, there's a *cough* reason why the Enterprise-E
exists, isn't there?