Select fire assault rifle in something like 5.56mm ammo like the M16.
Most of the armies in the world use weapons like that, even the Russians have switched to the 5.45x39mm AK74 and away from the .30 cal AK47.
Something like the M16 or AK47; accurate to at least 300m, yet recoil low enough to fire rapidly from the shoulder like a submachine gun for me to have the edge in close encounters.
It really is good for everything from zombies, to modern armies to alien invaders and with tungsten-core ammo it will work in a pinch against robots.
Logistically it is very good too, it is the most popular military cartridge in the world, popular with hunters too and a bandoleer of 10 fully loaded magazines equalling 300 rounds weighs only 10 Lbs so you can carry loads of it. For the same weight you could only carry half as much ammo in larger calibres like 7.62x51mm.
Shotgun shells are even more logistically unsound, as they weight up to 100 grams per round so a 10 Lbs bandoleer would be for only 45 shells. Many are not waterproofed at all so have to wade through water any ammo = useless.
Sniper rifles are in fact incredibly heavy for some strange reason, probably something to do with maximising accuracy and you need months of intense training as well as some inherent skill to truly take advantage of a snipe rifle.
Pistol or melee only if I wanted to avoid attention, but consider WWII, most of the casualties were unarmed civilians. In a similar situation I would not rely on appearing as unarmed to protect myself, it may just make me a more tempting target.
Automatic I suppose is like a submachine gun. Well an assault rifle is every bit as good as the best submachine gun only better in almost every way.
Special weapon. Rocket launcher would be nice, something like the RPG-7 or to be really retro the Super Bazooka [http://en.wikipedia.org/wiki/Bazooka#Rocket_Launcher.2C_M20_.22Super_Bazooka.22] that to spite the design being almost 2 decades older it has about identical capabilities.
Superweapon? Like a nuclear bomb? A stealth bomber? I suppose the closest thing to a super weapon you can actually carry is a Laser Designator to deliver precision strike of 2000lbs bombs. But I hardly have an advanced air force on call and this would be only useful for attack at a time when I'd be trying to avoid trouble, so no.
PS: I'd take the gravity gun if it was on offer.