I've gone back and forth on this forever and I've finally landed somewhere I'm happy with. For HD in my 590, I'm running Federal FliteControl 00 buckshot. The patterning on that is genuinely impressive, I got sub-10-inch patterns at 20 yards with my cylinder-bore 18.5" barrel. I keep the first two shells as #4 shot in case of a situation where over-penetration is more of a concern, then three rounds of FliteControl behind that. I also topped off with one slug on the lifter, one in the carrier. It might be overkill but I sleep better knowing what's in the tube..