It is a great weapon. You cant beat it for self defense, especially in a crowded area.
The 00 buckshot hits the hardest, but 4 is more than adequate for self defense. I like it because there is less recoil and more pellets. You cant go wrong with either. Anything coming out of that weapon will probably do the job, but 4 is the lightest I would use.
That is 4 buckshot.