For all you 00 buck guys:
Home Defense Shotgun Ammo
"Number 1 buck is the smallest diameter shot that reliably and
consistently penetrates more than 12 inches of standard ordnance gelatin when
fired at typical shotgun engagement distances. A standard 2 ¾-inch 12 gauge
shotshell contains 16 pellets of #1 buck. The total combined cross sectional
area of the 16 pellets is 1.13 square inches. Compared to the total combined
cross sectional area of the nine pellets in a standard #00 (double-aught) buck
shotshell (0.77 square inches), the # 1 buck shotshell has the capacity to
produce over 30 percent more potentially effective wound trauma. In all
shotshell loads, number 1 buckshot produces more potentially effective wound
trauma than either #00 or #000 buck. In addition, number 1 buck is less likely
to over-penetrate and exit an attacker's body."
I would take 16 .30 pellets over 9 .33 pellets any day.
The tradeoff there is that 00 is easier to find, especially in the more-appropriate reduced recoil shells.