I'm just going by reports several years ago, where our men would pick up enemy AKs because the reliability and firepower was preferable in combat.
There are reports of that. I've met some guys who came back from 'the sandbox' who said each weapon had it's benefits and downsides, but that the AK-series was overall better. Particularly if one lacked the logistical support provided by a well-supplied and organized military like the U.S. has. If you're on your own and operating independently, the AK is better. that's just anecdotal though.
I also think this post is illuminating.
http://www.ar15.com/forums/t_1_5/17...ounds__and_how_they_handled_at_our_range.html