If I had to choose three, it would be based on the current situation that I found myself in. If I had a "place" to go, whether my own home or a planned destination, I would take my Beretta 92fs 9mm. Accurate, fast, and non-jamming. Common ammo. Large capacity magazines. I would of course take my AR15. Good all-around bullet size for take down, mid-range accuracy, and talk about commonality with all of them out there. I prefer my mini-14 Ruger over the AR15, but for parts and mags, I would go with the AR. My AR10 would be my long range choice. I can hit 1200 yards accurate and still super-sonic 175gr and 185gr for reaching out and doing what you need to do. Downside, very heavy.
If I was on the move...Beretta 9mm. AR15, and instead of the AR10 I would take the Beretta CX4 9mm rifle. It uses the same mags as the 92FS. Capacity up to 32 round magazines, and gets me out past 100 yards with good accuracy. Little to no real kick, so the wife can handle it if need be while I use the AR.
The best weapon I have though, are my community ties. I live in a neighborhood, and have discussed my beliefs and concerns with all. Though I am sure some might think I am a nut, I would band them together to protect us all as a group. In my mind, this is the only way to truly survive something terrible. I have food for a bunch of people for a long, long time. I have more water than you could think of logically having. I have tons of ammo and guns. I have back ups to back ups. None of this really matters if I am trying to defend the castle alone. Will never work.