Definitely 505 basting spray, always spraying on the batting, rather than the fabric. It's a lifesaver. Have done safety pins, have done thread basting, but to me, nothing compares to basting spray. But I learned the hard way DON'T USE TOO MUCH - you need to use it sparingly, and cover anything you don't want sticky, including the excess batting that is around the periphery of the quilt top, and the surface that you've masking taped your backing to. Or "you'll be sorry!!" (sing song voice!)