re thread: My mother was very disappointed when Coats & Clark changed from making their standard threads cotton wrapped poly to all poly, and I have had a couple issues with the all poly thread on the new spools being wound tightly enough that it breaks in the machine instead of unspooling properly. But I tend to like the C&C better than Gutermann for ordinary sewing thread if only b/c that’s what tends to have the best color selection where I shop.
re: bobbins-- My sewing machine (Pfaff, c2000) originally wound bobbins to the point where the thread pushed the bobbin back out of winding mode; the motor has slowed down a little and now doesn’t get all the way there which leaves the bobbin thread a little bottom-heavy, since the top bit was always the last to fill completely. On my fairly cheap Brother that gets used exclusively as an embroidery machine, I have to stop the bobbins before they get to that point because winding them all the way will sometimes crack the plastic bobbins. When they come out wonky it’s usually because something was obstructing the path of the thread somewhat while winding, tho.
My Janome machine (2019) came with plastic bobbins, and constantly tangled. I tried the same size metal bobbin, and problems disappeared. Makes me think it was designed for the metal ones, and they subbed in the plastic to save a few cents.
I do make sure the bobbin winds evenly. That can make a difference!
I’ve been doing all my sewing on a 1951 Featherweight, so perhaps this is less useful info. It doesn’t seem to like Gutermann. 99% of my sewing in the last year has been with Coats and Clark 100% cotton, and aside from the fuzz my machine seems to really like it. As far as bobbin winding, again maybe my older machine doesn’t give much frame of reference, but slow and steady wins the race for me. (And I totally do the guiding it with my finger thing, too.) To be honest, the Featherweight doesn’t seem to care how neatly the bobbin is wound. All my issues have been with the bobbin case or an old needle.