Octopus

I am not talking about some rinky dink zoo Octopus. Obviously, between a normal sized shark and octopus, a shark is much scarier. However, a giant octopus would be the most scarcy thing imaginable, with giant, numerous suckers, 8 long and powerful tentatcles, a fierce and powerful beak, the ability to dispense large amounts of ink, and a just plain fearful appearence. No contest.