#4 Buck is the minimum buckshot load to meet the required FBI minimum penetration of 12 inches. See Box'o'Truth.
It seems like #4 buck would make a great home defense round -- more pellets, each with sufficient energy to be lethal, but less likely to penetrate into your neighbor's house and continue into your neighbor. Too bad it's so rare.
You want #1 or 00 buck. Collectors had Remington 00 in 25 rd boxes. I prefer Federal Loads as they come with either triple plus wad or the flite control wad very tight patterns. Hornady also uses a similar wad for their 12ga buck loads. Avoid the cheaper offerings for serious work. I have found the Premium Flite Control loads at a bunch of places recently, Bass Pro, Four Seasons, etc. I believe the Zombie Max is rebranded critical defense, and has the versatite wad.