I hate to tell you, but you are going to get as many answers as there are types of threads. What you want to look at is how the thread looks when you look at a piece up in the light. If it looks fuzzy (irregular, bumpy), it will do this in your machine and may cause problems. Threads and needle sizes need to fit each other. Best idea is to use the same thread in the top and the bobbin, and using same color hides a lot of mistakes. Now having said that, I love Isacord and King Tut the best. Isacord is slick (because it is a poly blend), and that makes it easier for me to remove when I have to rip out stitches. It is also excellent for embroidery. King Tut is beautiful for quilting. Experiment and use what works best for you and your machines.