I have both and here is my opinion.
Both games are similar in the sense that they focus on survival, and when you die you lose everything. This makes your life very valuable. In Day Z I can't help feel that my life is more valuable, and this adds to every experience in the game. Whether it be meeting other players, fighting zombies, and just generally trying to survive. Every experience is nerve racking as hell (more so than Rust) Some positives and negatives of both:
DAY Z:
The focus here is on looting, whereas Rust is more on crafting.
Pros:
- the in game experience (explained above)
- graphics
- some cool mechanics including handcuffing people, force feeding them poisonous substances etc etc
- players seem slightly friendlier (from my experience)
- TONS of loot including weapons and aesthetics (cowboy hats, glasses, and so much more)
- ZOMBIES (IMO)
- When you log out you are SAFE.
- at 6GB it's 6 times bigger then Rust. ( I guess this is a Con if you don't have uncapped internet)
Cons:
- Extremely buggy
- the controls take some getting used to and aren't user friendly
RUST
Based mostly on crafting, very similar to Minecraft. And more PvP orientated.
Pros:
- Smoother gameplay, less bugs
- Better controls - more responsive.
- Crafting is fun and rewarding
Cons:
- Lots of KOS (Kill on sight)
- "Sleepers." When you log out your character stays in game and essentially goes to sleep. During this time you are exposed to all
the elements including bandits. Can be disabled on servers.
- Difficult to progress out of the early stages of survival. Which can be rewarding or frustrating.
Summary:
I enjoy both games, slightly preferring Day Z for the reasons specified above. Remember both games are in their ALPHA stages so bugs are to be expected. I prefer CO-OP play and this seems more common in Day Z. If you love crafting and building then go with Rust.