[mb6606]

I'm hoping this will help me understand Hinge Action/Motion (sorry, as I'm still working on my terminology).

If two players wind up at impact separation with the clubhead, face and shaft in the exact same alignments all at the same speed and hitting the ball in the same spot on the face with every other alignment matching with the only difference being that one player arrived there after a Horizontal Hinge action and other player arrived there after a Vertical Hinge Action.

Which shot has better compression and why?

I think they would be the same.

They would have the same compression!
True VH allows only manipulation of the loft (layback) HH allows manipulation of the clubface to the left or right (no layback). In other words it would be easy to hit a high soft shot with VH and a low hook with HH.