I own a PSA upper kit on an Anderson lower, and a Norinco SKS, just one of each, and enjoy both. They both work fine, have not had any problems with either. The AR I've had for less than a year, the SKS was a $99 gun show score, so you can imagine how old that is. lol Both basic rifles.
When I say the SKS quality is "all it needs to be", I mean it's not necessary to change out parts, it works well as is. It's a bullet proof, no pun intended, design that works well for it's intended purpose as a combat rifle. No weak parts, no finicky design, and certainly nothing fancy.
As far as aftermarket support, there are hundreds of vendors online selling SKS parts. No, nothing like titanium take down pins to lose a couple of grains of weight, but any number of parts from any number of countries that will work.
The AR has had the advantage of being a newer design, but newer is not always better, and the AR had some teething problems initially.
While the AR has certain advantages of lighter weight and replaceable magazines, I wouldn't, as others have mentioned, feel undergunned with an SKS. I trained in basic with an M-14 and admit to having a certain affinity for wood and blued steel rather than plastic and aluminum. I think a butt stroke with an AR would be embarrassing and probably destructive to it. lol