Well, I'm no expert, but the gun I would grab for home defense first is a handgun. As for long guns, here's what I would grab, in order, if the guns went T.U. in succession (not counting nearly unattainable MP5s):
1. Rem 870 (or Mossy, Winchester, etc.) pump, short bbl, No. 4 buckshot, 12 ga
2. Bushmaster M17 bullpup, .223 (lotsa 20 rounders)
3. AK74-type (SAR2, etc) rifle, 5.45x39
4. My Mech-Tech Upper with G20 lower and Redfield Red dot. That's 10mm auto times 15+1, in a very handy setup.
Personally, I don't have #3 at present (SAR2), but plan to. I have the others.
Remember what people have said: The .223s/5.56 nato and 5.45x39 will apparently penetrate walls and endanger innocents LESS than a pistol caliber round or a 7.62x39 or 7.62 nato, so those small caliber centerfires would be the best choice, in all likelihood. The smallish buckshot in a shotgun will also ease overpenetration concerns, relative to a pistol caliber carbine. Notwithstanding that I have the 10mm carbine setup, I don't see much use at all for a pistol caliber carbine, truth be told, UNLESS its a stealth operation using a 9x19, .380, or .32 loaded subsonic with suppressor. Of course any .223s would work - AR15s/M4geries, AR180Bs, M17S, Daewoo K2, Galil, G36 clone, SAR3 or Saiga .223, KelTec SU16Bravo, even a Mini-14 in a pinch (after all, you're not trying to hit anything past 20 yards.
).
Bottom line here:
1. If stealth is a concern, suppressed 9x19 carbine with 147 subsonics.
(If stealth is not a concern: )
2. If overpenetration/innocents is a concern, and I anticipate a lot of shootin' goin' down, OR anticipate needing to penetrate SBA on the enemy, then something in .223 or 5.45x39. This is probably the best overall choice in the majority of urban/suburban situations.
3. If overpenetration/innocents is a concern, and I DON'T anticipate more than a few rounds needed (such as home defense), AND don't anticipate needing to penetrate SBA, then a 12 guage with No 4 buckshot or smaller, and extras in the sidesaddle.
4. If overpenetration is not a concern (no likely innocents nearby), OR I anticipate a high likelihood of having to shoot enemies through obstacles like small trees, walls, car doors, etc., then something in 7.62nato, 7.62x39, or possibly a 10mm carbine or slug-loaded shotgun (10mm or slug gun would be nice UNLESS I think I need to penetrate SBA - body armor).
Category 4 is ideal for CQB in theory, particularly 7.62 nato, because it can do it all againt the enemy - but it's only ideal if you DON'T have one of the other concerns: stealth or overpenetration/harming innocents/friendlies - and the latter is OFTEN a major concern. More I think about, more it seems that an AK74 type is purt near the best tradeoff of everything if you had to have just ONE, particularly on a budget. Now, get one of those nice bullpup conversions for it out of shotgun news, and I think you'd really have something! (though in truth, I think the conversions are for 7.62x39s only - bah). If you're really on a budget, a 12 ga with a pipe full of small buckshot or large birdshot, with 4-6 slugs in the sidesaddle *just in case* is a pretty decent solution.
There, now you have an excuse to get at least 4 different guns - you can thank me later.
Which knife is that Sulaco?