Thanks for all your help, I have deceided to miter them both. I did not know about sewing all the border rows together first, thanks for that idea. The miter corners are not that much fun to do, even though I like the look.

Thanks to everyone.

Oops. I'd better be on the lookout in case the quilt police come to visit. I'm just binding a quilt with a stripey border and I didn't mitre. Looks fine to me.