If you want to play the game for mods such as wasteland or dayZ i would pick arma 2, however considering further updates, developement, mods, etc will be implemented into arma 3, id pick that.
Im not really one of those guys to get too in depth when it comes to video games, for me arma 3 looks beautiful and apart from a few bugs i really enjoy playing it. I have fallen in love with altis life too. Despite the fact i keep getting banned -.-
Yeah, if they sorted the netcode on ArmA3 out, I'd probably move over to that from ArmA2. But, as it is, I find it pretty much unplayable in combat situations (most of the game). ArmA2's not great, but it's a lot better
Old when compared to today's gaming laptops and computers. I bought it solely for working but despite having 4GB of Ram and an Intel core I3 processor ARMA is far too laggy even on low resolution.