1) Better out of the box accuracy.
I'm not sure whether that's true of the new ones (assuming you're talking about a lightweight 16" AR, which is most comparable to a Mini in size and weight). But in general, the AR's much-maligned gas system makes a more accurate rifle all things being equal, and easy to strip and clean. I can't get into the constant bashing of the AR gas system; it has some real advantages over other semiauto designs.
2) Better support and modularity. You can do ANYTHING with an AR.
...except make it a quick-pointing gun like a Mini-14 is.
Still, I really like this feature of the AR. That's why I have an AR or two. The ready availability of a good-quality .22LR upper seals the deal, for me. Fun, durable, easy-to-clean, and cheap to play with.
OTOH, many people here ask which AR to buy, and have some sort of mental block about buying modules. They want to buy a rifle in a box. Especially given the price premium, I don't quite "get" that -- to me, 99% of the value inherent in the AR platform is its modularity. As a "rifle in a box", it's a pretty damned expensive little thing.
3) Parts availability. I have a spare bolt for my AR along with a complete trigger group. Try and get Ruger to sell you those parts.
Have you ever tried?
Those wouldn't be the parts I'd be most likely to carry for a Mini-14, but if for some reason you want to, Ruger will sell them to you AFAIK. For that matter, when something has broken on a Ruger I've owned, they've just sent me the part in the mail, immediately, no hassle, no charge. Try that with an AR.
The real upside of the AR here is the ready availability of upgraded parts from multiple vendors, like match triggers, different sights, etc. The AR wins this contest hands down -- not that these things are free, or even reasonably-priced much of the time, but they are highly available.
4) Magazines. Cheaper and better on the AR side.
The AR wins this one, for sure. Ruger should at least make factory 10-rounders for restricted states. It would help their sales, IMO. I'm going to try to get a 20 or two.
Again, I prefer the current factory Mini configuration for its excellent pointing ability and convenient carry in the brush. Without all the protrusions of an AR, it's a much more unobtrusive working gun to throw on a sling while concentrating on other things. The AR is designed to be used by someone whose full-time job is to carry an AR, and sometimes this shows.
Now if you do want a folding stock, the Mini will take one easily. Only a stupid-expensive AR can be fitted with a folding stock.
2) Might be more reliable in adverse conditions. I'm always suspect of any weapon that wears its guts on the outside as opposed to keeping gravel out of the action.
Last Sunday, I discovered another way to jam an AR. Somehow, a cartridge got stuck ABOVE the bolt. This doesn't and will not happen with a Mini. An AR relies on a precise mechanism working fine when it cycles; a Mini relies on a big spring slamming a loose bolt shut.
The idea that you keep the crud out of an enclosed action only works
until you get some in. Once it's in, it stays in. You can pour dirt
through a Mini-14, and it comes out again right away.