I personally prefer the 12 ga. 2 3/4" non-magnum standard load of 16 pellets of #1 buck (.30 cal) vs. the non magnum standard 9 pellet 00 buck (.33 cal) load for defense.

You get 7 more pellets, but not much loss of diameter.  I can't believe that a #1 buck pellet carries significantly less energy than a 00 pellet.

Looking for affirmation or argument....I want to hear your opinions!

suposedly they did a study a while back. I remember reading it in guns and ammo. The best round for self defense was Winchester 12 Ga. #4 buck.

I guess that's a good balance of size vs. amount.

From what I've read, the 16 pellet #1 is the way to go.  Best balance of pellet count, pattern, & individual pellet ballistics.  The #4 buckshot has issues re penetration (heavy motorcycle leather jackets, etc) & the #00 pattern isn't as good as it could be at range.  

I tend to use the same load.

I stick with 2 3/4 loads in general.  Shorter shot columns tend to pattern a little better in the same diameter barrel.  I don't care how many pellets I have, as long as I hit the target, but the #1 buck does it all.  For me, better patterns, less recoil and using 2 3/4 gets an extra round in the mag tube.  I like having an extra shot versus shooting 3".

I also like #4 too.  One time I got my hands on some heavy duty cardboard.  Big, thick, multi layer stuff, stiff as a board.  I set up a few torso sized pieces and had at them with #4.  In my case I had excellent patterns.  What stayed with me, was when we inspected the targets, the amount of shredded cardboard that just POURED out from between the layers.  Shredded is the only way to describe it!  So if overpenetration is an issue, the #4 will do a massive amount of tissue damage and I am sure cause plenty of shock to the target.

I like the #1 buckshot also.
The #4's may fail to penetrate, especially very heavy clothing, and the #00 may over penetrate in an inside-the-house defense situation.

Since my Remington 870 Police IS a home defense gun, I went with the #1 as a good compromise between the "cloud of shot" #4's and the "elephant buster" #00.

The International Wound Ballistics Association recommends #1 buckshot for many of the reasons already stated here.  Here is a nice article which explains it all:

www.firearmstactical.com/briefs10.htm

While my personal preference is for plated, hardened #000 Buck, I would be...and have been... perfectly happy with standard #1, especially if I deliberately wanted to get less penetration than the #OO or 000 but did not want to take the chance that #4 Buck would not be enough. (and after seeing several shootings involving #4 Buck I don't think it is)

I cant find #1 at anywhere near a reasonable price.