A short barreled AR15.
It's a reliable and accurate gun that, with good ammo, performs quite well terminally. Fragmenting ammo tends to penetrate fewer walls than other rifle rounds, some shotgun rounds, and most pistol rounds.(Before you act like a faggot and try to argue, google studies on the matter. Easily allows you to mount optics, a sling, a light, IR laser, etc. Extremely common ammo and parts, incredibly cheap these days. Can be concealed with a large overcoat, if necessary. Small enough to maneuver in a car if you have to defend yourself while going somewhere. For me personally, I spent a lot of time carrying and shooting one in the military.
Most importantly of all of these, it can be a very compact, very light weight gun, so your lazy, hungry, scared ass will carry it around with you instead of leaving it propped up against a wall or in the house. It's basically the perfect SHTF rifle.
As far as pistols, I like plastic 9mms. Lightweight, usually 17+ round capacity, common ammo, cheap, etc. I tend towards M&Ps or G19s, but whatever brand you prefer that is a quality pistol is fine.
AKs are alright, I enjoy shooting them, but they're an inferior rifle to the AR15, regardless of what some retard that watched the history channel in the early 2000s told you. If you must have an AK, the number one thing I will tell you is buy good ammo. Buy quality, American made, expanding ammunition. You'll see any issues you have with accuracy disappear, and will have a round that performs like a rifle, instead of a 9mm FMJ.
All of that being said, having any gun and some real training (Not fucking youtube videos of idiots that jumped in a ditch when getting shot at, or kicked out before finishing basic training) will put you ahead of the vast majority of the population.