The Mini-14 has two problems: 1) Loose stock fit with the standard wood stock. I don't know about their newer synthetic stock. 2) Rear sight blade wiggles too much.
Swapping out the wood stock for a Choate or Butler Creek sythetic will bring the Mini-14's groups into reason. This change alone will cut groups in half.
Also, using either a scope, or one of the aftermarket rear sights, or tightening up the rear blade will improve it even more. This can be done by putting a small blob of silicone rubber at appropriate spots in the sight, and still leave it adjustable. But a 2.5x to 4x scope will really improve this little lightweight rifle.
My Mini-14 Ranch Rifles, one with a 4x40, the other with a 3x-9x40 will do 1.5" groups with 55 gr FMJ.
With Federal Ordnance (now labeled PMI or Precision Magazine Inc.) 20, 30, or 40 round mags, or Ruger mags, these rifles are 100% reliable. They will function without cleaning far longer than an AR15, if you are lazy, and will do so even without lubrication.
For practical ranges, to 200 yards, shooting offhand, you will likely see no accuracy difference between the Mini (with the above improvements) and the AR. But by the time you do this, you are up into the price of a nice AR.