re: What kind of shotgun would you recommend?

I will say just because something is mil-spec, that doesn't mean it's good. Most high end ARs aren't made to mil-spec. They are made to a much higher standard.

In reality, the 870 and 590 are both hunks of junk compared to the M4.

To the OP, if you want the best home defense shotgun on the planet, buy a Benelli M4. There is a reason why it is used by elite forces all around the world. It is simply the best, and no one can dispute that.