I'm a newbie, so forgive me if I'm repeating something already on the thread, as I only read the last few pages.
Anyway, best for home defense, to me, varies by scenario and person.
Currently, I live in an apartment building. Maneuverability is a priority, as is avoiding overpenetration. I use my .45 HK USP with hollowpoints. Lots of knockdown power, but the .45 is a relatively slow-moving round, so overpenetration is not as big of an issue as it would be with other rounds of similar power. Also, exterior building walls are brick, so I really only need to watch my lines with regard to shooting into other apartments.
If I lived in the country and overpenetration wasn't a consideration, I might still use the same weapon, or I might consider something in a carbine. I haven't thought about it much, as it's been a long time since I lived in the country.
For my wife, a .45 might be too much gun, and she lacks experience with a shotgun, so I'd put a 9mm in her hands, which is something she's more comfortable with.
Ultimately, I think it's a largely academic argument. You could defend your house with a .22 against most intruders. It might not be lethal, but 10 rds of .22 from a Mark IV or the like would probably take the fight out of most smash and grab type thugs.