The AK47 and its derivatives are robust simple designs with generous tolerances, which means they can handle dirt, dust, mud, water, etc, without a hiccup. In 7.62x39 the heavier bullet has more energy to knock down steel plates (at ranges used in sport shooting).
The new ARs are more complicated designs with higher tolerances, which should make them more prone to failures if really dirty, but these days reliability is top notch. The dust cover over the ejection port also helps to keep dirt out. The higher tolerances deliver a more accurate platform and targets can be hit successfully further out, some claim 600 yards compared to the AK’s 400 yds.
Currently there are more after-market accessories available for ARs, but this is changing.
Whichever you select, both are excellent…