How to select which supernatural to believe?

[Neo-Scholastic]

I agree that this doesn't help one determine which prophets are genuinely sent by God. My argument definitely can't be used to prove God's existence as this would be circular: We assume god exists to determine which prophet confirms our assumption. It's only useful if one is convinced a benevolent God exists for some given independent reasons.

We can still narrow down the set of possibilities with very simple considerations: a prophet can't make logically impossible statements like the trinity (assuming Jesus really claimed this, and, arguably, he didn't). A true prophet obviously won't make a false prophecy. But let's say a self claimed prophet, let's call him Brandon, tells us he's from God and provides us with a book of hundreds of pages filled with all kinds of ancient wisdom and religious supplications, should we believe Brandon?

Obviously, if Brandon's book doesn't contain anything other than what anybody else can say or write, we have no good reason to accept his claim. However if, upon investigating the circumstances of Brandon's production of the book, we conclude that the contents of his book are factually true , unavailable to anyone in his surroudings, and can't be discovered by independent thought or any amount of creative genius, then this definitely increases the probability that he might be exactly what he claims.

If I am not mistaken you consider yourself a Muslim. As such, most of what you mention are IMHO secondary theological disputes (like the unity of God) that arise after initial first principles on which we already agree, such as, "only useful if one is convinced a benevolent God exists for some given independent reasons." What kind of independent reasons? Well, first off having reasons for a belief is not the same as having evidence justifying belief. The atheists, by and large, seem to believe that the subset of beliefs justified by evidence is superior to the larger set of reasonable beliefs. When it comes to natural science, I would generally agree with them; whereas when it comes to philosophy such an approach is questionable, to say the least.