I live in a fairly dense housing development myself (not as dense as you describe), so obviously I am not going to chose a .308 or 300 WSM as my primary HD gun (currently, that duty falls to my trusty S&W 686 loaded with 38+P). I am currently in the market for a 12 ga HD pump shottie, and from all the reading I've done online, the absolute bare minimum load I choose for a 18-20" shotgun would be #4 buck. Then again, I may just go with good 'ole 2 3/4" 00. #1 seems to be a good all-around choice as well. God forbid I ever have to defend my family against an intruder, my goal will be to stop the attack immediately and decisively.
I always get a kick out of the guys that load a whole variety of different loads in the primary HD weapon, escalating in effectiveness a bit with each round. I met a gent at the range once that kept his Ruger Security Six loaded with the following rounds:
Chamber #1: A brass shell casing with just a primer loaded in it (no powder and no bullet). Ya know, just to scare him away
.
#2: lightly loaded, wax bullet round. Just to sting the BG a bit if he isn't scared off by #1
.
#3-4: 38 Special snake shot. Escalate the stinging factor a little bit more
. Never mind that 38 snake shot isn't really effective past 7 to 10 FEET ... and that's against snakes!
#5: 158 grain 38 +P LSWCHP. Finally, we're gettin' somewhere (if you make it that far).
#6: 357 Mag (don't recall the weight or bullet type). Probably moot by this time.
So of the six rounds, to me, the only ones I'd consider effective were the last two. In a life or death situation, you may only get one shot. That first one had better count.