Animal Farm's pigs are bad leaders for a variety of reasons; all of which reflect the terrible nature of humanity or Mr. Jones to a worse degree.
1. The pigs lie to the rest of the animals. Many leaders lie for the best interest of the people, but this lying is for the betterment of the pigs. They lie about rations, about productivity, and about what happens to some of the other animals friends (like Boxer). The reason they lie is so that they can have more for themselves.
2. The adopt the problems of Man like drunkenness, slothfulness, and manipulation. The pigs used the extra money they made due to the work of all the other animals to purchase liquor.
3. The pigs change the rules to fit their own comfort and needs. They chose to educate only their young. They chose to alter the rules so that they could live in the human house, and be more equal than the other animals.