I love both of 'em, but I'll go with Zombieland. It's a thoughtless gore-fest compared to Shaun of the Dead (they're both not that gory) and I like that more in zombie movies.
A harder question would be Hot Fuzz or Shaun of the Dead.
Tag (Courtesy of Fkusumot) "If I'm posting in this thread then it's probally a spam thread."