If you are planning on playing any other zombie survival games besides Project Zomboid I advise you not to try WarZ I'm hoping the DayZ standalone will be something worth playing since the guys from ARMA are helping out.
I like zombie games, but I don't play them very often. Survival Zero looks pretty cool from the picture, I'll check it out soon – it definitely looks interesting.
I have, however, recently been playing an indie game called 'Zombie Grinder', it's pretty cool and still in the Alpha build stages. I've enjoyed the multiplayer gameplay and general feel of the game.
As for 'WarZ', I don't even feel like that should be talked about here.