The answer is there is no single answer. In some cases, even birdshot is the better choice. Keep in mind that not all birdshot is equal. This depends on your personal environment and home structure.
As for neighbors, depending on proximity they may not be a factor and especially if your home's extrior walls are brick or it is surrounded by block perimeter walls.
Often the penetration risk only concerns other occupants (chidren) of your house.
Most realize the risks attendant with failing to stop BG with the first shot, which can result from the use of a light load. When factoring in risks to other occupants of your home, consider the risk that they become victims should you fail to stop BG.
I opted for a graded load in my 12 gauge. My first round is loaded with super dense BBs, followed by three low recoil 00B, followed by a slug. That may not be the best load for others, but I like it. If I had to worry about my children's rooms being on the other side of the kill zone, I may opt for all BB loads.
As for those BB loads, I expect that they will penetrate two interior walls, but should that happen and an innocent be hit they will hopefully lack lethality. Remember, this is for home defense, which means close up and nasty. You may enjoy reading this http://www.thetruthaboutguns.com/201...arious-rounds/
The BB loads it tested were lead, but the Remington ulitmate home defense load I use is 10%denser than lead.