Well I never use polly. But if I did I would use gloss. It has nothing in it to "cloud" the finish to make it semi or satin. Then I would rub it out with punise to get rid of the sheen look often found in cheap furniture.
I see you commented about Cherry quite a bit and was looking for some advice. I built some bookshelves and applied a BLO to them and am about to put on a poly on, and was curious on your thoughts on glossy or flat for that? Thanks!