If you sculpt from the same distance and the same angle as A you should sculpt with A. If you sculpt with orthographic and directly from the front you should use B. Pretty much, match your FOV that you work in to your references.
For ZBrush, which of these two pictures should I use as the image plane for my sculpt? (this is from a CAT scanned skull) Thank you. A B (A is from the perspective camera directly facing the skull and B is using an orthographic camera directly facing the skull)