It depends on what you're into, if you want a huge map in which you can Role-play, play games such as King Of The Hill or you just generally are wanting to play on with your friends, fly planes and mess about with a huge selection of mods, buy Arma 3. If you want to be playing a game, where the main objective is to survive till the end, gathering weapons and progressing through the game, buy PUK's. Honestly, I prefer to play on Arma 3 as I enjoy role-playing, and on the odd occasion, playing with a few friends doing COOP missions and having a laugh. However, it is all dependent on the sort of game you're looking to play.