I have done both ways. It is a different look if you sew the borders together first and then attach. It is easier that way. And you DON'T have to Miter. The top borders just go all the way across the whole quilt. I think it looks cool that way. It makes it look like the border fabric. I am not good at mitering and I don't like dealing with all the bulk of the quilt when adding many borders one at a time.