Intermediate Range: Chuck Norris
Medium Range: Chuck Norris
Close Quarters: Chuck Norris
Sorry, I couldn't resist. On the serious side, I agree with the others, Mannlicher in particular that have said the 12 Ga. Shotgun, with a 8-9 shot capacity. A lot of people underestimate the versatility of the 12 Ga. Heavy shot buck would easily take care of individuals out to 120 yds or so. If in "your" area, I would also like an assault rifle in 7.62x39. It's got more punch than a .223. Compliment that by a pistol that you have a lot of practice with (automatic, revolver) in whatevery caliber you are good and proficient at. The pistol would only be my SHTF gun. Plenty of ammo for all three.
As far as tactics, the only thing I feel would give you an advantage in this situation would be if you were fighting in your terrain that they didn't know (streets, paths, buildings etc...) and to use guerilla tactics. If I was fighting for my life I would try to gain as much knowledge beforehand of the area I would be fighting in. I would plan traps, ambush points, choke points, and escape points. Guerilla tactics are frowned upon by more chrivalrous individuals, but their effectiveness is arguably the best way to go. In other words if given the chance, strike the most lethal and influential individual first. Then run to point X and plan to engage there. Strike at the next point and fall back to the next point, and so on and so forth. This would give you the best chance of survival and would help to cocnfuse and demoralize the enemy, and make them think twice before advancing because they are being taken out one by one. Unfortuantely, they are not very likely to all be bunched up in a group so you'll have to take that into consideration as well. Hit and run tactics. This would work even better if you had good friends/allies like eveyone says too. Hope you don't have to do what we're all talking about, but best of luck.