I use a 1/2" seam allowance and press open. I am a longarm quilter and that seam is the flattest one that doesn't deflect the needle as much as the 1/4" seam seems to. Pressing to one side creates a lump that goes all across the quilt, deflects the needle and I really hate them! If a customer quilt comes with a backing seam pressed to one side, I have to press the darn thing open so the quilting will nice and there won't be a lump.