It's been my experience after about 15 years of shooting all kinds of surplus and factory ammo both steel and brass case,reloading and casting bullets for the 7.62 x 39 cartridge that the SKS platform can be an accurate rifle if you feed it the ammo it likes,whether you have the time,money,patients or desire to experiment and fine out is a personal choice. Maybe you don't really care about all that and what to just shoot the cheapest ammo you can find in a centerfire cartridge.
As for me all the above was an still is important. When I bought my SKS rifles they were fairly cheap by todays prices,I gave like $149 for my refurbished 1970 Yugo M59/66A1 that I got to hand pick out of a full crate and I gave around $250 for a new in box Factory 26 Chinese SKS,to me the SKS is a poor mans M1 Garand,they are well made,reliable,easy to maintain and reasonably accurate out to 300 yds. if you feed it what it like. The SKS is a tool that for me may be called on to serve a variety of rolls.
SKS bores can vary after all they have the same twist as the Mosin rifles an some barrels were even made using old Mosin rifle barrel blanks. In general though you will find that most SKS rifles have .310 to .312" groove bores both my rifles have .312" groove bores so different dia. bullets shoot differently. As far as steel case surplus or commercial Russian ammo goes it's pretty much a crap shoot until you try it in your rifle,some might shoot well some might not and it can vary between different lots as well. I've tried many different brands of steel case and found that Golden Tiger FMJ or Bear ammo in FMJ,SP or HP all shot very well in my SKS rifles all the ammo was the lacquer coated steel case,the polymer coated an silver ie Zinc plated cases which actually used to be nickel plated have a tendency for the coating to start getting chalky or rust developing if they are not stored properly for long periods of time,
As far as the bullet used the majority are bimetal jackets ie steel jacket bullets with a copper coating and lead core,the jackets are also not bonded to the lead so cup and core separation often time happens which may or may not be a good thing depending on what you want the bullet to do. Also keep in mind that the HP's and SP bullets are more of a marketing function to sell ammo rather than actually preforming as those types bullets are usually intended to do. Sometime they do work as intended sometimes not,there are lots of variables that will determine if thats the case,velocity an what they actually hit,in general the closer the better as at some point impact velocity want overcome the steel jacket an your basically shooting FMJ bullets at that point. With ammo loaded with bullets made by companies like Hornady,Federal,Remington,Winchester,PPU etc. those bullets are designed to work just like any normal hunting bullet at 7.62 x 39 velocities. So you can buy what you know works or just take you chances. Most all the ammo I shot as well shot to different points of aim so that something to be aware of as well if your switching form one brad to another.
My personal preference for plinking,target shooting and hunting are cast lead bullets I cast myself. The bullets I cast and use most are the Lee 160 gr. RNFP,Lee 185 gr. RN or a custom mold I purchased from NOE that cast a 160 gr. FP bullet all are of the gas check design. I also have a good stockpile of Hornady SP's and V-MAX bullet that I bought in bulk many years ago for 8 to 10 cents each. I also load my own 150 gr. SP's bullets made by Speer,Sierra and PPU,those along with the Lee 185 gr. cast bullet are my close range bush busters. One of the benefits of reloading my own ammo is that I can tailor they ammo to each rifle although the different rds. I settled on seem to shoot about the same in both rifle cast or jacketed. The cast generally shoot lower at long range but that an easy holdover adjustment once you shoot them a lot.
So in general in my rifles if I'm shooting steel case ammo it's going to be GT FMJ or Bear SP's
For general purpose plinking and shooting I shoot cast lead.
For hunting it can be either of the heavier cast lead bullets,123 or 150 gr. Jacketed bullets.