Hmm..
An ergo design of some sort, where you can support the prongs with your fingers, since its easier to keep the bands square with the slingshot then, to prevent forkhits. I like a medium- to- narrow fork, about 1,5" space between the prongs, you still have to flip it, but its not so narrow you have to concentrate more on avoiding forkhits, than to aim.
I only shoot butterfly, and this is what i prefer, but i think WCDB is right, you can do it with almost any kind of fork
/Matt