If you believe the films, it would be a never-ending battle if dinosaurs and humans had to coexist. But, as with animals today, some dinosaurs would have been dangerous, and others would have been harmless …at least if left alone. We would probably be a bigger threat to them than vice versa.
The most dangerous would surely have been the meat-eating theropods, like Tyrannosaurus and Giganotosaurus. These animals were the size of buses, with heads the size of bathtubs, and an average human could have fit into their jaws. But many of them, particularly Tyrannosaurus, were also intelligent animals, with large brains and keen senses of smell, hearing and vision. Our best hope would be if they found us too small to make a satisfying meal.