In
animal farm, what is the primary difference between boxer and benjamin ?

 Boxer - the workhorse. He believes things will get better if he works harder and trusts the pig leadership will help him. He is considered the metaphor for the common people in Russia whom believed the Revolution and overthrow of the Russian monarchy would help them. They are trusting and easily manipulated like Boxer. 

Benjamin - the cynical goat. He has seen the cycle of power struggles and knows that nothing will get better with the pigs' leadership. He is never really happy and trusts no animals but Boxer and loves him until Boxer is taken away to his death. 

Similarities: Both animals are controlled by the pig regime whether they like it or not. Both find friends in each other and try to make best of what they have