Depends, you're going to have to be more specific than that.
By sheer statistics, it's of course humans. If we're looking at animals, then it is probably some kind of an insect like a mosquito because they spread disease and kill a lot of people that way. If we're only looking at large animals, then probably something like a shark. Really depends on what you mean.
We are animals! Sharks are hardly dangerous (we all have to eat)... most people who are attacked by sharks survive; we're too boney for their taste. Free Willy is a hell of lot more dangerous than Jaws. And don't think for one minute that Flipper is a saint!
But yes, no doubt we are.