Day Z has a janky ass engine.
Rust has horrible hit detection , lag , hackers and they can't seem to figure out how not to make servers shit themselves after a few days of everyone building massive structures.
H1Z1 so far is having launch pains. I need them to get these and server issues sorted before i can say how far along it is. I was getting pretty bad performance yesterday but they said it's because some servers had fps issues. I'm hoping that what it is.
Because of SOE, the size of their team and their proven engine H1Z1 seems like the one most likely to be able to pull it off one day. I have no horse in this race as I put 400 hours into Rust legacy and loved it but it's still far too early to tell who will be the better game at the end. I hope one day all three of these games reach a respectable 1.0 because it's a great genre with moments that none of others can replicate.
As janky as DayZ's engine is I still think that after another year of development it won't be any worse than the Arma games. Combined I've probably got 1500 hours in Arma and it's just one of those things. I'm hesitant to say you get used to it because it implys the interface is bad. For some things in Arma it's necessary, like independant head movement, it's janky as fuck to try and use but (I think) it brings a lot to being in an FPS perspective.