I am another one who loves my sweet 16. I have yet to have it complain about any thread I have thrown at it. Yenmet metallics, superior invisible poly, king tut, aurifil, guterman, isacord, yli, and I can't remember the others! Any good quality, strong thread will do as long as you get comfortable adjusting the tensions. I generally use superior's Superbob per-wounds in the bobbin, just because it is easy.
pam