I usually do a 2 or 3 stitch backstitch. BUT, I also bury the tails.
Just leave enought to thread a needle. Then "weave" the needle in and out of the batting without bringing the needle up thru the quilt. When you get about to the end of where you think your thread is....bunch up the fabric, bring the needle up and cut the thread. Once you straighten/flatten up the quilt, the thread is hidden