Just last week I had squares that I sewed together to make long strips for a border and when I pressed the seams open - unless you're right on top of the seam you can't see the seams. I'd worried how "visiable" the seams would be but they weren't and I was using a solid, which I was certain was sure to want to show the most.
I don't have a preference, I try to do whatever I think will look best on the quilt.