Vampires. Faced with destruction, they would sacrifice those pussies from the Twilight series and infect some humans with the badass vampirism from The Last Vampire or Bram Stoker's Dracula. Zombies, even if they were willing to attack fellow undead, would be easily destroyed by those superhuman vampires.
Robots are cool, but most modern robots are stuck on assembly lines and vacuuming floors. I don't think the robots are currently organized enough to produce more robots, so I think they would be disassembled by vampires. Or zombies would get goop all over the robots, and they jam up.
Or in another possible scenario, no one wins. Zombies only feast on living flesh, so undead vampires and metallic robots do not tempt them. Vampires see no threat from zombies, and let them live. Robots, presumably solar-powered, wander around during the day and vampires come out at night. It's a tie, with this trio of soulless species crushing all humans.
Except me, 'cause I'll totally be a badass vampire. Or a vampire cyborg.