I use a blind hem stitch, but I don't butt the 2 pieces together. I stack them, cut a nice straight edge, pin and stitch with the straight part of the stitch to the right and the zigzag part to the left. Then I open it up and rub my finger along the seam to smooth it out. I love how it comes out and you can not tell where the seam is when it's done. I find it easier to handle this way than to butt them together - especially if the pieces are large.
I used to put them side by side with an overlap, cut a wavy line and hand stitch the pieces together. It comes out nice that way, and you would never know it was pieced, but can be awkward to handle. I prefer the blind hem stitch way best. Try a few ways on some scraps and see what you prefer!