Interesting...
I don't have a dog in this fight, having examples of both in my collection.
There is a big takeaway and an implicit corollary deduction you might be tempted to make
The Big Takeaway: tighter tolerance between bolt and carrier and receiver (or dust shield for those rifles that use such a thing like the FN) are actually better for reliability, since they keep the crap OUT.
The implicit corollary: internally low tolerances tend to be less reliable, especially in a dirtier internal environment.
I say that last because the AR got a rep, in large part because the early Colt models exhibited poor field reliability in service, but also because of the direct impingement system. I note that I have an FN-FAL that has been "accurized" (LaFrance) and it's fussier on ammunition, according to LaFrance "due to the tighter headspacing", so I'm sticking with this corollary.
As for my AR, which is actually a nice Bushie, I've never had so much as a hiccup, but then, it is babied.
As for your subject line, I'm assuming people get really partisan about their AKs and ARs. What a silly waste that is, since it is best to have all of the above.