I've found spray basting has a very firm hold with no shift. I spray my batting and then unroll the back onto it, flip them spray the batting again then unroll the quilt top. Pressing and smoothing as I unroll. I've used pins on small things and I hate them, always in the way. And if you use straight ones they poke you, and if you use safety pins you have to stop and unpin them as you go. :evil: Mean pins. I think I've been poked everywhere!
Oh and I've done spray basting with full, queen, twin, and doll sized quilts. My next challenge (for later this week!) is a king!