I would think there is no definitive way of defining an animal smarter than another but humor me.
Bonobos, chimpanzees, bottle nose dolphins, and elephants are on my radar for the smartest animals.
Does anyone know which of these animals are the "smartest"... a list in order would be awesome.
Some facts I have learned about some of these animals:
chimps and bonobos are the closest relative to the definitive smartest animal... humans
bottlenose dolphins have been seen to display empathy, communicate in complex manners, use "names" for themselves, and use tools
elephants have culture in the form of burying their dead, moving disturbed elephant bodies to spot of death, staying around dead (relative or non-relative) long after they certanty of death, and they have also been seen to protect other animals and humans from danger or help them when in distress
I find advanced intelligence of other animals very interesting.