I would rather have a mini14 that I know will for certian will perform, than an ar15 that may not. although most ar15s with chrome lining are usually pretty reliable.
murphy's law is quite evident in gunfights. after watching combat footage from iraq and afganistan you get to see just how unreliable some of those m4s over there can be at times.
In a law enforcement firefight if you are going through 20 or 30 round magazines you must be taking on the Hell's angels. Anyways the magazine changes are no more difficult than from an ak47. rock and lock.
One could say the ar15 can have problems with magazine changes as well. how many times have magazines dropped out of an ar15 that a soldier thought was fully seated.
the mini14 is light. It points and shoots quickly. In a close quarter enviroment those are some pretty decent characteristics.