Sig 556 or Adam Arms upper on AR 15?

[klover]

I steered clear of the AR 15 platform in favor of the AK's mainly because of the stories of carbon fouling.

Now for around $1000, I am thinking either the Sig 556 or any good lower with an Adam Arms upper in 5.56x45 may well be a better rifle than a top line AK in the same caliber. If you AR guys could suggest reasons for the Sig over the Adams, I would love to hear your reasoning.

No re-hash of either of these verses the AK is needed at all, since those are apples and oranges.

Thanks for your time.