Does wearing NV or SG in the face slots work better then attaching them to the helmet or does it not matter? Does is confer the same bonus regardless no matter where its placed?

Wearing them on the face gives a better bonus, since the helmet slot is only for storing. Whether you use the helmet slot or an inventory slot is irrelevant, unless the vision item is on the face, it won't give any effect.
P.S. You can also use Shift-N (and Ctrl-Shift-N) to automatically switch goggles for the whole team, if I recall correctly Shift-N switches the goggles, Ctrl-Shift-N selects the appropriate ones for current time.