The accurized AR15s are not exactly "sniper rifles", wonderfully accurate they can certainly be but that little 223Rem makes them more like a varmint rifle.
The better guns will generally give a box stock Remington 700 of the same caliber a run for it's money accuracy wise, it's just the AR platforms do it for more money. Benefits are definitely the lighter recoil, ease of loading, not having to carry loose rounds to reload after every 5th shot, and a few other things.
All of the high volume manufacturers make AR15s that are pretty accurate, between a Bushmaster Varminter, an Olympic PCR with a Ultramatch barrel, an Armalite Target variant, DPMS bull barreled gun, or a Rock River version, it's likely they will all turn in subMOA performance with good ammo.
At some point, one of the manufacturers is going to offer something that the others don't. Either it will be something style oriented, physically different, or value based that winds up helping you make your decision. It won't neccesarily be capabilities that set the rifles apart because they are all fairly closely matched.