Personally, I don't think there is just one best. First thing you need to do is maybe figure out what 'type' of AR you want, and then look at what the manufacturer offers. Decide on barrel length, bull barrel vs normal, free float barrel or not, collapsible stock or not, flat top or iron sights, ect ect and then decide the manufacturer. Of course, I don't know anyone personally who only owns 1 AR, so don't think you need to knock yourself out figuring out what you like. Do what I did, buy 4 of 'em.
16" M4 clone or 24" Varminter, I would go with a Rock River.
The Bushmaster V Match is a nice calling rifle, and it was my 1st AR.
Armalite, Bushmaster, DPMS, Rock River....I have seen, owned, and shot them, and they are all fine.
There are others that are are rumored to have very good quality, but I don't have firsthand knowledge so I will pass on commenting.