I was always told......cotton on cotton on cotton. That means cotton fabric, cotton thread and cotton batting (like Quilters Dream Cotton Batting). I always use a neutral threads also - beige for lights and greys for darker tones for. I prefer Mettler products and also YLI 100% Cotton Long Staple Thread, 40/2 ply. I get a lot of my YLI from Red Rock Threads on line.
American thread is not made as well because it has short fibers in the thread and can break easily. European threads are better and stronger because the fibers are longer. I've been quilting since '96 and was taught all of this and firmly believe this information. These are for piecing. For quilting the tops I go crazy and use Mettler Polysheen because it is strong and the threads won't snap (unlike rayon).