Which was the fiercest dinosaur?

The tyrannosaurs certainly look the most fierce of all dinosaurs, but in terms of overall cunning, determination and their array of vicious weapons it was the dromaeosaurs that were probably the most fierce of all. Utahraptor a recently discovered dromaeosaur measured about 8 metres from head to tail and had very long arms, with wickedly hooked talons for claws to grasp its prey; a large head and sharp, curved teeth, a long balancing tail for running swiftly to pursue its prey, and powerful legs on the end of which were huge sickle-shaped retractable talons. These dinosaurs were very powerful, highly agile and intelligent predators, nothing would have evaded them, and if they hunted in packs then they may even have been able to bring down large sauropodomorphs.