Thread is a personal quilter's preference. Use the thread you and your machine like and the thread you can afford. You could invest a small fortune in thread and I haven't found it necessary. I save my special threads for special projects and use polyester thread on all of my everyday and frequent wash quilts. I have not had polyester thread melt, break or cut through quilting fabric as some quilting rumours have reported. I had a friend give me a whole bag of polyester thread that she was sure wouldn't work for her quilting and I've been happily using it ever since.