This honestly sounds like you not having seen nearly enough NC to make a judgment and me not having seen nearly enough AVGN to make a judgment. What little I have seen from AVGN makes your description of the Nostalgia Critic sound much more like AVGN, frankly. There are very few reviews where he "can't go two sentences without shrieking, wailing, and/or flailing his hands and arms around" - these are not what I would call defining factors. And NC is an extremely expressive person.
Anyway, yeah, let's not dive any further into the annoying Nerd/NC debate, because it always seems like nobody on either side has opinions that are representative of actual fact. I shall carry on.
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Recorded B8 Mafia record: 13/24