I like a stop border and usually make it 1/2 to 1" finished. For the next border, I have various methods.
1) The final quilt has to be a certain size, so I add borders to make it that size
2) I only have a limited amount of border fabric left, so that's how big the border is.
3) The border fabric is a print, and I want a particular portion of the print to show.
4) I use the scientific audition method. I sew on the narrow inner border, lay the outer border out & move the quilt back & forth.
As a mathematician, I prefer one of the above methods to Fibonacci Sequence. I think making it pleasing to your eye is the best.