The AR pattern rifles enjoy a much larger market of parts and accessories. I like the Mini too, but earlier versions were known for accuracy problems - particularly as the rifle heated up. I think the current version has had most of those problems dealt with, but the AR is so much easier to work on, like a snap-together model. Magazines for the Mini-14 tend to be more expensive (for good ones that work) and in shorter supply. They do not interchange with the AR-15 mags.
If you're only going to buy one, I'd recommend the AR. Have a look at Windham Weaponry; they're the same people who started Bushmaster.
I had a 181 series Mini, which did fine until I put an aftermarket flash suppressor on it. Then the accuracy stunk. I removed it and it shot well again, even hot. Likely an adverse effect on the barrel harmonics was the cause.