um, probably a killer whale.
even sharks are afraid of them, plus they're extremely intelligent and have their own sonar language.
It's important to be something at the top of the food chain so you don't have to live in as much fear.
edit.
although the negatives of being a killer whale is getting kidnapped by stupid capitalistic/money hungry humans who want to put you on display so that you die prematurely. Then when you lash out and kill one of them they'll just blame you as if they didn't steal you and put you in a small ass fishtank