If I have to piece a border, I determine a quilting design that will end up with a line of stitching right in the seam. It really makes it so you cannot readily see the join. If the quilting design is going to be straight across, then I do a straight join. If I want to do a diagonal quilting design then diagonal join.
Sometimes I put an element from the quilt top into the border so the design comes out to the quilt edge in a couple of spots that totally disguise a border join.