Pieced Backing - Vertical or Horizontal?

I've seen so many fabulous pieced backings out on blogs lately, I just had to try it.  For one purpose, it was because I didn't buy enough backing.  For another purpose, it was to add block fabric from the front.  In any case, I usually sit there for a while trying to figure out if I should go horizontal or vertical.  On the one where I did not have enough backing fabric, I had no choice but to go horizontal.  I worried the whole time that it would not be straight.  Luckily it worked out.  On the pink backing, I had a lot of blocks left over from the Blush Lap Quilt finished in February.  This one needs to be assembled with the quilt top yet.

What's your preference if you piece a quilt backing?  Is it to save on backing fabric or to use left over quilt blocks?  Do you randomly place them or go in a straight line?  Here's what I ended up with.

On the blue T-Shirt quilt backing, I added horizontal swimsuit blocks to the back and brought in border strips.

On the Blush Lap quilt, I'm going to go vertical with the pieced blocks.  I'm going to try and offset the front blocks strip to the left of the quilt top backing.

Thanks for stopping by!
~*~Trish~*~