IMHO, AR's are much more varied, "component" wise. The AR has WAY more individual parts than an AK has. So as such, the quality of the AR is only as good as it's weakest link (You'd want, at least, "decent" parts for EVERY AR part to avoid problems). Due to the greater number of parts, and prices for each, price has an inevitable role in it's reliability.
The AK, however, has MUCH fewer parts, and most of those parts remain combloc built. Combloc countries tend to overbuild their parts, so they're pretty much all extremely durable and reliable is properly built. With the AK, you seem to pay more, primarily, for "feel" (smoother, better machined, etc), where as an AR's price reflects more serious differences.
My Russians ran great and were smooth as butter. My Romanians ran great and were... well... not so smooth haha. But they BOTH worked flawlessly and do their job. Is the better machining and smoother "feel" worth the extra? Only you can decide that, but either way you'd have a seriously reliable and heavy duty rifle in your hands.