As much as I enjoyed reading all your replies, I’m disappointed that I did not get any help.
I was really trying to fathom whether jelly or peanut butter is better once the sandwich is bit into depending on its layering.
I guess I’m looking for the why is one way better, over the other.
I can accept that it is answered by those who see no difference, or mix the two ingredients.
Let’s say you have peanut butter on the lower slice, and jelly above it, on the upper slice, as you take a bite. Before you initially shift the bite to chew you are mostly protected from tasting anything but the bread. The force of the initial bite may squish the looser preserves out the edges of the miniature sandwich, sending fruit flavor to the sides of the tongue first.
I think THIS is the deciding factor. Whether the preserves are top or bottom, the more liquid quality they have means they are likely tasted firstly, after the bread.
That may unravel the whole question.
On the other hand, perhaps the upward movement of the jaw for the initial bite could cause the reverse order (jelly on bottom, pb on top) to have a hydraulic effect on the loose peanut butter. That is, the quickly moving jelly, moving towards the roof of the mouth, pushes some peanut butter out the sandwich bite first.
For me the answer is I’d rather have the sweeter jam taste happen first, then be followed by the savory flavor of the peanut butter.
So, I vote peanut butter on the bottom.