ORIGINAL: Retaks
We always have used No.4 Turkey loads for fox and coyotes when hunting with shotguns. I knwo we are allowed to use buckshot but we know how are guns shoot with the turkey loads already so its easier to just use them.
I suggest trying the MOD choke first, on the theory that buckshot generally (but not always!!) patterns better from a moreopen choke. An improved-modified or even a cylinder bore might work even better. BUT, since #4 buck is pretty small, you might find that a tighter choke will be satisfactory. But I would not use a real tight tube to begin with anyway, for ANY size buckshot.