I've found that the more expensive brands tend to offer greater reliability/durability.
That said I don't think dropping an extra few hundred dollars for larue or moveske is worth it, my 700 stag model 2 has run great for a few years now, including some hard running weekend courses.
Honestly most ppl don't run thier ARs hard enough to notice the difference anyway.
Best bang for your buck would be bravo company, if you can find one, but a S&W or stag is just fine.
...if you can find em