I have an R15 carbine in 223. In this photo it is equipped with an EOTech 552 for low light hunting, but I've since changed it to a Leupold Mark AR 3-9x scope, which is more suitable for all around coyote hunting.
Accuracy is excellent. It will cut 1" groups at 100 yards with bulk remanufactured ammo, and half inch groups with premium ammunition and handloads.
The gun balances very well. It may be a tad light at the muzzle for some folks. In that case, I suggest the slightly heavier R-15 rifle. The carbine has an 18" barrel, which is a very good compromise between a 16" carbine and a regular 20" rifle. It has a bit more velocity, a bit less noise, and the gas port is moved forward two inches over the carbine. This is called a mid-length carbine. The gas pressure at the gas port is roughly 9000 psi less, and the recoil impulse is closer to a rifle than a carbine. There's less battering of optics. You can, though, accomplish about the same thing by installing a heavier buffer, like a 9mm buffer. (The R15 rifle has a 22" barrel, by the way, and gives more velocity, yet still isn't as awkward as the 24" barrels. It also has a mild report compared to even the 20".)
The barrel is fully free floated in an aluminum free float forend. If you use a bipod or sling, this does not put pressure on the barrel. The barrel itself is a medium weight. Note that there is no difference in accuracy with a quality heavy target barrel or a quality lighter barrel for the first couple or so shots. It's when the barrel starts to heat up that the difference becomes apparent. The R15 is NOT a varmint gun, meaning it was not designed for high volume fire. It was designed with coyote hunters in mind. In my opinion, this is the ideal barrel for that purpose. The barrel beyond the gas block is fluted. This does not add strength. Frankly, it doesn't really save much either, because the flutes are rather shallow. At best it helps cooling not from increased surface area, but from the bottom of the flutes being closer to the bore, allowing faster cooling of the inside of the barrel where it is hotter. This supposedly helps the barrel not shift as quickly. I do not know if this is a contributing factor to the accuracy of this gun, but it certainly does not hurt anything.
There are no sights on the R15s. They are designed for optics. However, Bushmaster makes a folding sight that can easily clamp onto the front gas block, and there's a whole raft load of rear sights, from fixed to folding. This means primary or backup sights can be installed, or at least the rear can be carried, or iron sights can be installed to cowitness with a red dot or EOTech.
The trigger is single stage, and is very nice right out of the box. It's good enough that I'm not going to change mine for a match trigger. Note that the Bushmaster version of this rifle (in 20" and 24") comes with a two-stage match trigger, which is why it costs more. Because the R15 trigger is a smoothed up AR15 trigger, it does have a long takeup compared to a bolt action. Creep is very little. Break is clean. It's glass smooth.
Reliability has been flawless. Because I use mine for hunting, I mainly shoot 5-round Bushmaster mags in it, which ain't cheap (about $30 each). They've been reliable. (Oregon regs restrict centerfire semi-autos to 5-rounds for all hunting.)
Finish. The R15 is camo dipped. I've had mine long enough, and have used it enough, to have some wear. The pistol grip is worn and chipping. I'm going to order a replacment. Some of the camo film is a bit thin on the edges around the front of the mag well, but it's still intact. The forend has a slight sheen to it from hand oils where contact is normally made, but this is common to any camo dipped gun.
The gun fits me quite well ergonomically. It comes up fast, and eye alignment with the scope is right there, using 1" height rings (as measured from the top of the rail, which is actually a Picatinny, not a Weaver, to the bottom of a 1" scope tube). There are plenty of positions to set a scope up for proper eye relief. I prefer my scope back more than most people, because I have neck alignment problems and can't crane my head forward. For the ultimate in adjustment, the R15 carbine is also available with a telestock, which can be set to different positions for length of pull.
If you want a semi-auto for serious coyote hunting, this is it.
One thing I would not do with the R15 is use it for plinking. The R15 is a hunting rifle. Get a cheaper gun or better yet a cheap upper for that, so you don't have to worry about burning out the throat. Oh, and that's another thing. The R15 has a 223 chamber, not a 5.56 NATO chamber. I only shoot 223 ammo in mine. I have other AR15s for burning 5.56 ammo.
As for a Mini-14, plinking is about all they're good for, with the exception of their target model. If a Ruger product is really wanted, get the Ruger SR-15. But it will cost more than an R15.