I use both Steam-A-Seam (regular and lite) and Wonder Under and love both. It all depends on which I have on hand and when the last sale at Joann's was, which is when I usually stock up. Steam-A-Seam can be a bit trickier. If you don't use the right amount of heat and steam for the right amount of time, it may not adhere as well. For projects that will be used and laundered frequently, I stitch the appliques down with a blind hem stitch.