First off, my apologies for being a resident of California.
I'd agree with everything Ugly Gun said, with a few reservations.
For home defense a shotgun is superior, it is the single most powerful and effective self defense weapon readily available. In terms of effectiveness at stopping a person, rifles and pistols don't come close to the effectiveness of a shotgun. For home defense you want a shotgun. To use the often repeated expression, you use your handgun to fight your way to your shotgun.
To better answer your question it would help if we knew what sort of all out assault you were planning on. In a riot, I'd want an assault rifle, why? Intimidation, and I'd have it decked out to look mean and scary.
The problem with the matter is that all guns are best suited to specific roles. A handgun is there (or should be) 100% of the time. It is a short range weapon, of limited power (even a .45). A Shotgun is a slightly longer range weapon, with devestating power. It is useful to about 100 yards, more if you're using slugs. It is versatile and has less threat for penetration than even a .223. It will almost ALWAYS knock them down in one shot (presuming you aren't using slugs). An assault style rifle, like the AR-15, is designed for medium range. It is the most versatile of rifles. 100-300 yards or so for the AR-15, though it can be used at greater ranges if certain conditions are met. A Bolt action, with a good scope, is ideally suited for longer range work, 300-1000 if your accuracy is up to it. Problem is most fighting isn't done in this range. Doesn't mean you don't want one. You want a handgun, shotgun, assault rifle, and long range rifle.
For more information on this sorta stuff, try these sites:
http://www.easley.net/warlord/gunz.htm
http://www.FirearmsTactical.com
the first one has survival type information, the second will tell you a lot about firearms ballistics, penetration and that sorta thing. They recommend #1 buck shot if I'm not mistaken to minimize penetration, while still getting enough penetration to really mess the badguy up.
-Morgan