I want to use bunny tails in the border and had originally envisioned having the border be eight squares wide, but thought I would see how it might look at four squares wide (that is, with sixteen patch blocks). Yikes. It clearly over powers the bunnies and doesn't even look like tails.
With the help of a seam ripper, I tried out the look of a nine patch border. It still doesn't work for me.
A little more reverse sewing, and I think the four-patch wins. There will be a floating border that will come between the bunnies and the four-patch border...the size of that will be depend somewhat on what will make the four-patch border fit and turn the corner nicely.
And if you're thinking that I have a rather slap dash method of testing out borders, I would have to agree with you. But I use my design wall under constant peril.