The gun YOU buy is only important based on who you're going to use it on in your fantasy scenario.
If you're going against the liberal college kid that's gonna bust into your house and rape your wife and ten daughters for drug money, a standard semi-auto AK-47 is perfect. I'd suggest the night sight, so you can take him out while he's climbing your chain link barbed wire fence. Auto conversions, clips over 60 rounds, and bayonet attachments are just overkill.
If you're going up against the BATF because they want to take away your freedom to collect other weapons and stockpile wives for the day Jesus returns, I suggest forgoing a gun and investing in an RPG-7 or handheld mortar.
If you're going up against the Islamic terrorists hiding out at the local midwest Planned Parenthood clinic plotting to douse your compound with sarin gas, you DEFINITELY want something automatic, with armor piercing capability. A LandWarrior is great for this, and the "bunker buster" fuel-air grenade attachment means you can take out the clinic as well, doing the Lord's Work for a 1000-point bonus at the pearly gates.
If you're going down to your local schoolyard to revenge yourself on the thuggish classmates who beat your pencilneck ass with your loveworn copy of The Fountainhead, I suggest a good Remington 10- or 12-gauge shotgun, sawed-off and filed for maximum distribution. A semi-auto mod and 12 round clip means you have just enough time to spout one-liners or Chuck Palahniuk quotes between discharges.
Lastly, if you're gonna safely pimp strut in da hood like a white OG, straight ballin', it's all about the NINE -- the Glock 9mm, ceramic barrel. Word.
If you're just shootin' varmints like any good ol' bored-ass redneck in Podunk, Texas, then just get yourself a .50 caliber black powder bolt-action rifle. It fuckin' DIS-INTEGRATES 'em, man. Sooo-eeeee!
If you're just buyin' a gun to feel tough or cool, then STOP. Don't buy a gun. Buy a fuckin' KATANA down at the local mall cutlery store, because it's just that much more fuckin' HARDCORE.