1973 904 for 360

Why does everyone have a crazy strong opinion on what fluid to put in a mopar 727 / 904 . Shouldn't this just be a fact ? Literally everyone has listed every type Trans fluid out there as " the one " to use .
Guy who rebuilt the trans who works for / owns local ammaco shop for last 40 years insists on " mopar 4 " but we couldn't find it so he said " atf+4 " is second best choice . But again I want to use what is best for the trans o don't care what the answer is but how can it be " dextron " and "type f " and so on.