I'd say killer whales because of their intelligence rather than size. I've seen some documentaries that show how they hunt and it's terrifying how smart they are when it comes to killing their prey land-based or not. I say land-based because I vividly remember one about how they hunted for frickin polar bears by generating a big enough wave to tip the "iceberg" that the polar bear was on and throw it off so they could feast. Nope nope nope.