The mini-14 did have its problems with accuracy. Not that it wasn;t accurate, just that there were other rifles (M16 and M4 for starters) that were more accurate. I know because they were the standard longgun for the Border Patrol for many years before being replaced by the M16 and, eventually, the M4. We had to qualify with them out to 100 yards, and they were an acceptable deadly weapon....just not a sniper's rifle.
The mini-30 is a different beast. It's strange to hear so many tout the SKS in a way that makes it appear it's a "MUCH better" weapon than the mini-30. If that's your opinion, it's surely allright, but I would differ in a fevered way. For the SKS to be better than the mini-30, OK...maybe, depending on the opinion of the user, but even if so it doesn;t stand apart in a grand way. Again, both of Ruger's mini-hi powers (14 and 30) are essentially the same things as the Garand. For those who haven;t fired, disassembled, cleaned, and reassembled an M1, well, you might not appreciate the simplicity and reliability of that design. I'm not saying it was the best rifle ever made, it surely wasn;t, but Ruger picked it to copy from for a reason.
The mini-30 is a short, heavy, .30 cal cartridge. Anyone expecting good accuracy out of a "carbine" round, whether it's a mini-30 or an SKS, is kidding themselves. That rifle was never designed for sniper work...however well the barrel is contructed and with whatever rifling, the round just isn;t fit for the job. Hence the popularity of the 30.06, .308, and .50 caliber. Now THEY can reach out and touch someone (especially the .06 and .50 cal). The 7.62 x 39 is just a medium range killing rifle and the mini-30 is no exception.
Ruger took steps to improve the accuracy of the mini-14 (and maybe the mini-30, IF that could reasonably be done), but they didn;t do it so much because the rifle was inherently inaccurate, but more because they wanted to reach the competition market, I think.
Preference between the mini-30 and the SKS is just that, in my opinion....preference. I own and shoot them both and as I read the posts in this thread, I think there is no bias on my part toward one rifle or the other. They're both good guns and if one is slightly more accurate, I would think it's just that particular rifle, not the entire line.