Originally Posted by MTS

I think it really depends on the fabric.

If your choice of border fabric is a solid/blender type, and will be densely quilted, it really doesn't matter. The seams will disappear either way.

If it's a print pattern where it will be very noticeable (and you didn't have enough yardage to cut the borders lengthwise), I'd go for the option that is more pleasing to the eye.

And if that means I have to do a straight seam, instead of a diagonal, because it looks better, or I'm trying to match the pattern up, then I would opt for that.

Because of fabric shortage (poor planning on my part), I have had to hand stitch the strips to match the pattern - I fold it over and "applique" it to another strip so I'll have the needed length for the border strips. Almost impossible to see the seam line.