World War Z without a doubt. The book was an amazing slow burn of a novel. The fear gradually built up until you were afraid to put it down. The zombies were the traditional slow zombies with no reasoning capability. The action occurs over weeks and months and years.
The movie, if you had never read the novel was actually not that bad. It was frightening and suspenseful and gory.
The problem is that they had absolutely nothing but the name in common. And the names of some of the characters. I knew years before it came out that it would be a travesty, so my hopes weren't very high for accuracy. My son however was heartbroken. You would think after paying that much for the rights they would have at least attempted to follow the book.
Yeah, didn't happen.