it really isnt 2 types of AR, just that based on certain geek's preference, they would like a Single-sided or Double-sided AR coating on the xtals.
heres a single-sided Taka AR xtal installed on my 112H. theres still some reflection on the crystal but lesser light reflection as compared to one with no AR.
while this is a Double-Sided Taka AR on my previous Sinn U2 GMT. notice the invisible glass effect it has on the watch?
the more recent genuine Panerai series of watches comes with a single side AR if im not mistaken, thus a single side AR is the way to go if you wana conform to gen-like.
however the older generation of Panerai might not have AR coating on their xtals as per gen buy some geeks for preference sake still prefers to have either a single or double sided AR on theirs.
well it all boils down if you would prefer 1 or 2 sides?
Cheers!
Ash