I have used aurifill 40 and 50 weight, YLI variegated, isacord, king tut, yenmet metallics, guterman, and others I don't remember! As others have said, the S16 is not picky about thread. You do have to get used to adjusting the tension, but you should pick threads you like that go with the designs you use. The S16 can pretty much take them all; it is just a matter of you getting comfortable with the tension (both bobbin and top).
Pam