Is it the thread that is breaking? Is it the fabric coming out of the seam? I would first look at the thread, then the stitch length. I piece with my machine set at 2.0 and have not had seams come apart. I do chain piece, sometimes with leaders and enders. I also strip piece, so backstitching at the beginning and end would not help. Also, quilts that are tacked or tied have more stress on the seams, during use and washing, than a quilt that is machine quilted all over.