Which positive and negative character traits are exhibited by some of the animals in Animal Farm?

There were animals on the farm who truly relished the opportunity to live a life of freedom from man's oppression and were quite prepared to make the necessary sacrifices for the good of all concerned. One such animal was Snowball, who displayed a number of positive character traits in his approach.

After the Rebellion, it was he who encouraged the animals to spring to work, as indicated by the following extract from chapter 2:

"Comrades," said Snowball, "it is half-past six and we have a long day before us. Today we begin the hay harvest. But there is another matter that must be attended to first."

He played this role until his expulsion. He was always hard at work motivating the animals and played a central role in organizing the farm. He, for example, created a number of committees and was tireless at organizing them, as we read in chapter 3:

Snowball also busied himself with organising the other animals into what he called Animal Committees. He was indefatigable at this. He formed the Egg Production Committee for the hens, the Clean Tails League for the cows, the Wild Comrades' Re-education Committee (the object of this was to tame the rats and rabbits), the Whiter Wool Movement for the sheep, and various others, besides instituting classes in reading and writing.

Clearly, Snowball was unselfish and had everyone's best interests at heart. However, a negative characteristic was that he, much like the other pigs, accepted that they were entitled to certain privileges from which the other animals were excluded, such as their claim to the milk and windfall apples. This suggests an air of superiority and goes against the principles of Animalism which expounds equality and fairness. This supercilious claim to certain benefits is mentioned in chapter 3 when some of the animals complained about the unfair distribution:

At this some of the other animals murmured, but it was no use. All the pigs were in full agreement on this point, even Snowball and Napoleon.

Boxer, too, exhibited hard work and dedication. He was committed to giving his all for the farm, as we read, also in chapter 3:

Boxer was the admiration of everybody. He had been a hard worker even in Jones's time, but now he seemed more like three horses than one; there were days when the entire work of the farm seemed to rest on his mighty shoulders. From morning to night he was pushing and pulling, always at the spot where the work was hardest.

Sadly, though, one of Boxer's negative characteristics was that he became too slavish and seldom questioned Napoleon's motives. Being the strongest animal on the farm, and the fact that he had the admiration and respect of the majority of the others, meant that he could have easily taken charge and opposed Napoleon's later dictatorial rule. His simple-mindedness prevented him from so doing and he, instead, adopted the maxim, 'Napoleon is always right,' leading to continued abuse and, ironically, his death, at the hands of the selfish, uncaring and greedy pigs when they sold him to the knacker.

Benjamin, the donkey, had the intelligence and ability to oppose the pigs and defend the other animals since he was just as intelligent as them - a positive trait, also mentioned in chapter 3:

Benjamin could read as well as any pig, but never exercised his faculty. So far as he knew, he said, there was nothing worth reading. 

The extract suggests that Benjamin adopted an apathetic attitude. This negative trait suited him perfectly, but if he had applied himself better, he could have introduced changes that would have benefited everyone. He could have challenged the pigs when they changed the commandments. His careless attitude displays some selfishness on his part and he, as mentioned in the following extract from chapter 3, remained much the same throughout:

Old Benjamin, the donkey, seemed quite unchanged since the Rebellion. He did his work in the same slow obstinate way as he had done it in Jones's time, never shirking and never volunteering for extra work either. About the Rebellion and its results he would express no opinion. When asked whether he was not happier now that Jones was gone, he would say only "Donkeys live a long time. None of you has ever seen a dead donkey," and the others had to be content with this cryptic answer.

One could cynically suggest that Benjamin was too clever for his own good and maybe for the other animals too. 

One could also refer to Napoleon and Squealer in this essay. The former had a commanding and controlling nature, which resulted in his leadership of the farm. He was blessed with a natural ability to take control, a positive characteristic, but unfortunately, he was overwhelmed by a selfish desire for power and authority which lead to him abusing the animals for his and his cronies' benefit. In the end, his tyranny was even worse than that of Jones and his men. 

Squealer had the 'gift of the gab.' He was a persuasive and vivacious pig, able to convince others easily - truly a positive trait. It is sad that he did not put this talent to better use. He, instead, chose to manipulate the other animals and propagate Napoleon's abuse. Since he was such a brilliant orator, it was easy for him to spread lies and deceive the animals into believing whatever he told them, to ensure their acquiescence and silence. His greed and loyalty to Napoleon became a paramount factor in the abuse of all the other animals.