Most professionals recommend 00 buck in reduced recoil LE versions like Federal Tactical or Winchester Ranger, Rem. reduced recoil, etc. Check out Ammoman.com.
Be advised that the new Fed. LE 132-00 has the FliteControl wad that tightens patterns considerably---like 7 to 9" at 25yds! The Fed. 133-00 8 pellet load would be good for HD. Remember that at close range fighting distances, no buckshot load has time to spread into a pattern. Be precise, as if shooting a slug (also very effective).
All of the reduced recoil LE ammo produces tighter patterns with far less recoil than over the counter buckshot loads, which are high vel. and recoil. Street results show that low vel/recoil LE ammo gives up nothing in stopping power. Excellent stuff.
If you go to a #4 buck load, be advised that you are cutting down on penetration and increasing innocent bystander safety while decreasing stopping power as well. Decisions, decisions. Stay away from birdshot, since once the mass of shot actually becomes a pattern, the individual shot have no penetration and are easily defeated by heavy clothing, or living room furniture. Even #4 buck suffers, to some degree, from the same disadvantages.
000 buck has excellent penetration and 8 pellets are standard. However, the penetration may be excessive and 000 doesn't pattern as well ad 00 buck. Taking on a bear at close range, it would be my choice (just behind slugs). I think LE has the right idea with 00 buck, and wish we had more street data on #1 buck, as well as a LE version.