I may have mentioned this, but my wife's birthday is approaching. She has asked me to run a zombie game for her and some of our friends. I have two zombie roleplaying games on my shelf: Dead Reign from Palladium (which is actually my wife's book), and All Flesh Must Be Eaten from Eden Studios.
I have run AFMBE a handful of times over the years, always as one-shots, and it has never failed to be a good time. However, my wife doesn't particularly enjoy learning systems she is not familiar with, and since it's a one shot, I'd like to keep things as simple as possible. To that end, I was considering using Dead Reign, which I have not run before. (My wife didn't buy it for the rules, by the by- she bought it because she loves all things zombie.) Palladium's rule system is a little closer to what this particular group of gamers is used to: d20 to attack (roll high), d20 saving throws (roll high), ability scores in the 3-18 range that are very similar to D&D stats. We have hit points, level, even alignment. I think it is more similar to what they know. Dead Reign also has several varieties of fully statted zombies, as opposed to the AFMBE "Zombie Buffet" creation rules.
...ah, but then there's the skill system. JB, if you are reading this, I know you're nodding your head in assent.
If I had more time to do this and less on my plate (I've also got work stuff coming up for the coming school year), I'd probably just use Fudge or Savage Worlds and be done with it. However, I like that these games have zombies all statted up and ready to go. I think if I were going to run a campaign, I'd probably go with AFMBE.