For hand applique, I use the Mettler Silk thread, which is 100% cotton. Why they call it "Silk" is anybody's guess. It is a 50/2 thread. The finer the thread, the less visible it is. I have also used silk thread, which is 100 weight, and it is almost invisible. I would not recommend using DMC unless you are doing a buttonhole stitch.
For machine applique, I recommend a 40 weight polyester thread, like the Superior So Fine, if you want to see the stitching. If you don't want to see the stitching, use a monofilament thread with a 60/8 needle.