it really only makes a difference how you piece your back if you are going to have the quilt (long-arm quilted) if that is the case it is better to have the seam running horizontal instead of vertical. when there is one seam running from top to bottom no matter where, middle or off set it builds up when the quilt is loaded on the bars causing the sides to be (floppy) but if the seam runs side to side then the seam lays nice and flat along the bar, no build up of layers to cause problems. but if you are quilting it on a home machine it doesn't make much difference how you put it together.