I use a guitar pick because of the simple fact that I seem to always lose them, so they are cheap and readily available in plentiful supply. It is 0.38mm thick. I have experimented using sometimes the blunter corners which are normally on the "held" ends of the plectrum to get a rounder fuller sound.
Kenneth -- To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
