Glossy. Absolutely. When it was first issued to you, it was shiny. Now, it is dirty and worn, but it still has that "I was glossy, shiny, and new once" look to it. I put 2 coats of glossy white on my HIPS before weathering. I did a few extra pieces unglossed just to see what it would look like and there really wasn't any comparison.
The gloss shows through just enough to make it seem "real".