The two most widely used would probably be the 3" 4 buck and 3" copper plated BB's. There is also the Hevi-shot "dead coyote" that comes in 3" T shot BUT at $30/10, not as many guys use them.
It would be best to also take the time to pattern your gun as some guys have found that more open chokes pattern better and some guys find that the tighter chokes pattern better. Basically, every shotgun is different and each needs to be patterned to find the most effective load/choke combo.