There is no one supreme God amongst Avatars or incarnations of the second person of the Trinity.
But if you want you can consider either one of them supreme according to your preference.
As an aside, I find the idea that one must make a serious effort to decide accurately how the ranking for supremacy among exalted deities somewhat peculiar.
Why would such a need exist? It is not like the Devas, Avatara or understandings of the Abrahamic God are in some sort of competition for supremacy - or that it would fall to humans to arbitrate such a competition if it even existed!
Or so I would think, anyway. Am I missing something there?