I prefer the Sta-flo liquid. You can adjust how soft or firm you want the fabric. I mostly use 1:1 ratio. I put it in a spray bottle and spray the fabric as I go. Some people get upset because it can flake BUT the flakes brush away and when you wash the quilt the starch is removed in the wash.
I especially like to starch the quilt top and back before loading on the longarm. They load easier and straighter and the quilting goes along without a hitch.