Having virtually no experience with AK's. For the 7.62x39 round, assuming it's a semi-auto; I prefer the SKS.
Have built AR's and bought some too. I like the build option for experience, and the pride associated with putting something together that's as satisfying as an AR. But builds involve choices, and any one of them can go sideways and provoke unnecessary stress and delay. This is especially important when making choices that affect cycling reliability. These days I build only if it's something I can't buy, or can't afford to buy; and even then I try to stay inside the original design parameters where the system internals are concerned.
Buying seldom has the same pitfalls, since builders offer warrantees and go to some trouble to test their options choices; so reliability is a high priority in such situations.
Having tread those roads, and looking at your intentions for the implement in question; I would make a different, simpler, and usually cheaper option, one that may have an additional benefit as well.
You want to have semi that delivers a relatively high rate of fire, carries a respectable amount of fodder, and I'm assuming you want something compact, yet bread and butter familiar in your hands. I suggest the Ruger
PC Carbine. Versatile with a capital "V", it uses common pistol magazines; Glock 30rd among them. It can even be tricked out into something awesome.
Mine shares magazines with my
Ruger American Pistol 9 Pro, a full size military pattern striker/polymer pistol with up to 10/17rd capacity, depending upon your jurisdiction.
This is a very basic and simple firearm; and that shows in its outright reliability, IMHO.
Both handguns are utterly reliable in my experience. If as you suggest, you want it to serve an additional duty as a 9mm HD firearm, consider the terminal performance of a 124gr Federal HST round, as opposed to something of the 223 variety. If there was a requirement for distances beyond 100-200yd, I'd be favoring the 223. But since you're more interested in plinking and HD, the 9mm is very available, relatively cheap, likely more terminally effective at short distances than the 223, and can be loaded with many sorts of purpose-designed rounds. For defense, I have Federal 124gr HST, and for practice, IMI 124gr JHP. With a dot scope, this firearm is very quick to acquire a sight picture, and is steel plate accurate to at least 100yd.
Since my collection of magazines can be pressed into service for both the handgun and the carbine, I only need to buy once/cry once, and currently have a couple of handfuls of 17rd magazines for my ensemble, which is how I see it. Originally purchased to serve for 2-gun combat matches, it's my choice for shorter distance courses; and I have another rifle, an M4-gery, for distances beyond 100yd. I am developing handloads for it employing the
Speer 75gr Gold Dot LE Bonded/protected soft point.
I use my 21 y/o Grandson, and 23 y/o Granddaughter as my no holds barred test crew. They are given target, a firearm, and ammunition at a formal range; and I watch and see how they deal with it. This Carbine and Handgun combination was s recent example. They figured out the operating sequence, loaded up, sighted in, and were hitting targets quite reliably in a very short period.
They ended up smiling, and had no handling or equipment interruptions.
Plus, the carbine is a takedown, and fits in a 24" sling pack. Not a phantom lightweight, but not unreasonably so. That mass is mostly in the blow-back bolt, and tames recoil as can be seen in the "something awesome" video. The visible "recoil pulse" is actually the effect of the bolt returning into battery.
Greg