Length-
I like to have a good bit of stick showing on a bun, but forks make that less important.

Measure your buns, say the three go to styles. (in my case the two I know )
Add around a half inch for functional prong length, and I tend to go at an inch over the bun diameter.
I find the fpl of a fork can be less than a stick. Sort of like how a pair of shorter sticks will hold like one longer one.

And I found jeters better for looser buns, too. So I'm experimenting. I've been of the tight bunned mean ladies club for a while.