I am a stickler for cotton thread. On my LA I use King Tutt and Aurifil after a lot of trial and error. I have been told I can use any type of thread on my LA but I find KT and Aurifil both work best with the tension. As for piecing I use cotton and poly. I'm still trying out all of them. I guess it's a learning curve and it's whatever works best for you. There is no hard fast rule. You need to take into consideration the type of batting you use on each project with thread and tension. (And we think this is fun!!!). Ditto to CKCowl's comments.