Gutermann is nice and I have a few spools but I'm an Arufil convert thanks to this forum. Tried one spool and fell in love! My favorite thing about it is that SO MUCH fits on a bobbin. Nothing worse than running out of a bobbin mid-seam! I also have a large cache of C&C thread that I'm trying to use up. My Janome doesn't seem very picky at all but I definitely notice more "fuzz" with C&C.
My machine came with a bunch of Robison-Anton thread (and that's what my dealer recommended, she was horrified to hear I use C&C) but to me it doesn't seem all that much superior. Decent stuff, don't get me wrong, I'll use up what I have, but it seems nearly as fuzzy as C&C to me. *shrug* I guess I'm just addicted to Aurifil now and nothing else will excite me!