I have used a single border of 12", as well as multiple borders that are of different widths (i.e -1 1/2 /3/4 1/2 or 2/4/6). I have made "checkerboard" borders and piano-key borders, ice cream cone borders and scalloped borders. Some people use complementary fabric, or contrasting fabric for the borders. Whatever you want to do, you can do, because it is your quilt.