Fastest one for me is the jelly roll quilt. I sew strips end to end until the length is what I want the quilt width to be. Then sew the strips together. Be sure you sew strips in opposite direction to keep from bowing. Right to left, then left to right. Keep going until the finished size suits you.
To avoid having the seams right next to each other, you can cut off a few inches of one strip to remedy that.
It takes only a little longer to sew end to end at an angle instead of straight across. It does look much better this way.