The AR is perfectly reliable assuming two things:
1. You buy quality (RRA, DPMS, Bushmaster, Colt, Armalite). The AR design is less tolerant of sloppy assembly and out of spec parts than, say, the AK. Get a good one, though, and it will run like a top.
2. You maintain the weapon. You don't have to go nuts with the cleaning, giving it a good going-over after you shoot it each time will be fine. Just don't expect to be able to neglect it for thousands of rounds and months on end before hosing it down with brake cleaner. An AK will probably tolerate that. An AR probably won't.
The AR is more expensive to get and run than an AK, but (if you take care of it) it will be perfectly reliable, more accurate, and more ergonomic (subjective). The M1A will be a lot more expensive to get and run than either, but it should also be reliable if you take care of it, and it has a harder hitting round.
Any of the three will work for casual shooting and home defense.
Mike