Gutterman mostly because joann's is close, but have used mettler, coats, madiera, connectingthreads, all with no problems. You don't have to use cotton to piece, it is an old myth. They have a lot of nice poly threads these days. I use whatever's handy. I haven't seen to much difference in lint among the brands I use cotton thread is lintier than poly anyway, plus I am a notoious cleaner after I sew.