Zombies vs Unicorns is actually an anthology of 12 stories dealing with either zombies or unicorns. Holly Black is the head of 'Team Unicorn' while Justine Larbalestier is the head of 'Team Zombie'.
Each story is given commentary by the editors at the beginning about the pros and cons of zombies and unicorns. While the deciding factor is up to the reader, their comments and debate are hilarious.
Out of all the stories, I enjoyed "The Care and Feeding of Your Baby Killer Unicorn" by Diana Peterfreund, "Bougainvillea" by Carrie Ryan, and "Prom Night" by Libba Bray. Not that the others weren't also great, I just enjoyed these three most of all.
The only thing missing was a story of zombies and unicorns fighting each other...