Summed up, the Mini is hands down the most reliable of the two rifles and is a wonder of simplicity. It will, however NEVER shoot as accurately as the AR-15. You could spend another $500 to tune up a Mini where it will approach the accuracy of an AR but........... if that is necessary, why not buy the AR in the first place?
Flash
The Mini is the more reliable?
I've shot quite a few tactical rifle shoots back in CA, and some people favored the Mini because it was "CA-friendly" right out of the box.
The number of AR malfunctions I saw that weren't due to ammo or operator error was low, considering how many ARs we saw. The number of Minis that I saw make it through a 100 round match without a malfunction is zero.
There was one that would basically turn into a bolt-action rifle midway through the first stage, but I think he was having magazine issues, or one of the many mods he'd done to the rifle just wasn't working out.
Thats probably a bit of an exageration. A .22 upper or conversion kit is going to cost you several hundred dollars. . . which is a lot more than just getting a .22 rifle.
The calibers, there is a lot, but they are all relatively similar (except maybe a .458 socom) and pretty expensive. And again, the uppers will cost you $500.
I'm not arguing against an AR (I'm drooling over a 6.8 spc upper), it just isn't the cheapest way to go for a multi-caliber platform)
Dude, not all of the caliber options are similar. You can go from .22 LR to .50 BMG!