I have used rayon thread on a wallhanging but it is not as strong as cotton or polyester. I wouldn't use it on a bed quilt because you will probably get some breakage from sitting on the bed and general wear. I have not used wonderfil so I don't know if it is stronger than the thread I used for my wallhanging. Your top is beautiful and I would use a machine quilting thread. As for the best brand of quilting thread, that is really what thread your machine likes best.