OK, do you want mitered or not? If you want straight borders do you want horizontal or vertical? Would you accept a cornerstone block at each corner - this could be a part of your quilt design highlighted or not? What effect do you want overall?
I do my mitered borders as one piece as it is much easier to do. I can fold one edge back to line up the different borders, iron, and pin as needed. Because I start with what I can see the borders work. If you felt better you could glue baste the underturned part and baste the seam first to check it out.