H1Z1 is very simiilar to PUBG, DayZ is a whole lot different. I prefer DayZ although the devs are slow as hell. People will tell you that DayZ is dead and will never be finished, but that isn't true. It is just a very slow dev process, and one of the main reasons I think early access games shouldn't be allowed. But they are finally going into beta soon. As for what you should get, it all depends. Do you want more gameplay like PUBG? If so go for H1Z1, if not go for DayZ.