I read all with interest on many levels, but I think most posters miss the basic point.
He is not asking what the best Home defense weapon is for in the house. Sounds to me like he has that covered.
He is asking what to use if things go really south. Laws, legal ramifications, moral consequences to the side, If I am sitting at my house, what rifle do I want to use to defend it.
While I am not going to sit and drink myself to death thinking about it like Pat Frank, I must admit it is something that has crossed my mind as well.
All that said, back to the original question, and it was also touched on here, I think by the original poster.
I would add a couple thoughts.
1. I think the most important thing in that scenario would be Ammo more then rifle. I want something I can sustain myself with ammo, if that was through reloading, buying bulk, getting military ammo etc. that would be my first thought, guns without Ammo are just kind of big sticks. My approach would probably be 30-06 and reloading capabilitites.
I believe (I do not have facts to back me up) but I believe that the 30-06 round is one of the most common out there.
2. I would not want a semi or a black gun or an AK etc. etc. except maybe as a last ditch. The reason really ties back to the answer above. When your adreneline is up and rushing, you will go through bullets at an incredible rate. Everyone want's to portray themselves as calm and cool when the crap is coming down, but the reality is that most folks, even the best in the world, tend to fire LOTS of ammo in a fire fight. I don't think many of us here on this board do the practice and training that many of the guys that we picture and think of in these scenarios do all the time. I think with a black gun you may find yourself with a stick in the first 3 minutes of a fight. Might be all you need, but it may go 4 minutes, and bringing a stick to a gunfight is no fun.
3. I would like to have a black gun too the side if the situation gets dire, but from the $ comments made etc. I doubt a black gun and the ammo to feed it and the ammo to practice with it are really in range. It is what I would grab second.
4.I have the cheery thought that fortunately for me, my next door neighbor, whom I do nothing with, but he is in the employ of someone that has sticks that reach WAY out there

While we may not be aquaintances, we share a common interest in preservation and I think his stuff will reach a lot farther then mine will
Good luck with your decision. Let us all hope that none of these things ever come to pass.
Edit, while yes, he said "home defense" and most folks seem to take that in the context of being "in the home" I took it too be more of "homestead" or "property area" which is why he posted about the fields, animals etc. If I read incorrectly, my apologies. (and I am in the Shotgun/ pistol crowd)
Also, if you do not get the Pat Frank obtuse reference, look for the book Alas Babylon written where I grew up, still interesting reading today.
Got thinking about it a bit more, and wanted to add this thought as well on ammunition consumption.
Go play paint ball. Play serious, count how many balls you shoot. Limit yourself to X number. While it is not realistic in some ways, the ranges are a lot less and that would probably be where I would want a semi anyway, I think you will be amazed at how fast those balls disappear. I think my kid went through 1000 balls Sunday.