Most, if not all of those rifles have been arsenal reconditioned. All parts showing to much wear have been replaced. I have only heard of one with a bore problem and it was a worn muzzle on one of the earlier rifles with a non chromed bore. The fellow that owns it, counter bored the muzzle 1/2cm and all was well.
I haven't seen any others with counter bored muzzles, maybe others have. It may be something to look for.
They all seem to be functional, reliable and have similar accuracy. Look at as many as you can and pick the one that appeals to you the most. If you like the looks of one better than another, buy it. It will be a lot of years before these rifles appreciate in value to any great extent. Buy at least one or two crates of ammunition with it and learn how to clean out corrosive salts from the primers.
The SKS is a very decent little rifle. You will either like it or hate it. It's heavier than it looks but balances well and comes up to the shoulder like a dream.
It was designed for rugged use and the European models were machined rather than stamped.
If you are looking for a collector piece, Look for as many original parts as possible, such as non ###X stock numbers, chrome/non chrome bores, black/gold/bright bayonets, painted or blued receivers. Also look for the refurb square that is stamped on the cover.
I've seen several that are claimed to be unissued but I don't believe it. There may be the odd one out there but that would be like finding an unissued Garand or Lee Enfield. They are definitely not easy to find. Many dealers, not Lever, advertised them as unissued. They didn't bother to mention that they were unissued after refurbishment.