i typically base my decision on whether i want the border to be one piece or not. if it needs to be one strips the borders are the first thing that i cut.
the quilts for myself, i don't mind if i have to join 2 strips together in order to achieve a length long enough for the border.
the quilts that i sell or enter in competitions, i never join 2 strips together to achieve the length unless its a pieced border and a design element.