From various estimates of intelligence among animals, it’s clear that primates rule in the smartness scale, at least on this planet.
Of the top ten, seven are in that category.
However, keep in mind that primates came up with the concept of being measured, so maybe you should take this ranking with a grain of salt.
Here’s how they stack up:
Chimpanzees, including bonobos
Smaller toothed whales, especially the killer whale