Humans. They are very useful.
I'm really impressed with their intelligence, and fascinated that despite that, they still have hard lives! I watched a video where some scientists did an experiment, and they showed the grudge-holding against particular people passes through at least one generation! The baby crow learned from his mom and remembered the lesson on his own.Lately I've become very found of ravens and crows. They are incredibly intelligent birds. Have complex languages (distinct dialects, 'hand' gestures etc) , can memorize human faces and hold grudges against them (even warn others about them), and they always give me a laugh when I watch them try to drop rocks on the neighborhood dog that's been bugging them.