I have a Gammill, and through the years, my son and I have come to agree that the same thread top and bottom works best. That makes us put a back on a quilt that we might not otherwise use, so that we won't have glaring differences front and back. But I am not a professional contest entering quilter, so don't use my word as the last word in quilting. I guess if I ever get to that point, I might have to re-think my methods. But, for me, right now, yes, always use the same thread top and bobbin.