Snowball represents the upper class.
Snowball was one of the pigs. Historically, he was Leon Trotsky in the Russian Revolution. He was one of the original leaders of the revolution until he opposed Joseph Stalin and Stalin had him killed.
In the fictional world, Snowball operates in much the same way. As a pig, he is one the privileged class. He gets to eat the milk and apples. However, he does sympathize with the little guys of the lower class, in this case the rest of the animals. Snowball is a visionary. This is represented by the windmill.
The animals had never heard of anything of this kind before, … and they listened in astonishment while Snowball conjured up pictures of fantastic machines which would do their work for them while they grazed at their ease in the fields or improved their minds with reading and conversation. (Ch. 5)
Snowball is the true communist. He believes in Animalism, and wants the animals to be organized into committees and working together. He really does want them to have a better life. The windmill is symbolic of that. While Napoleon sees it as a way to distract the other animals and keep them working so they don’t see what is really going on, Snowball really believes it will make the animals’ lives better.
As with most idealists, Snowball never saw it coming. He opposed Napoleon, and no one opposes Napoleon. As soon as the plans for the windmill were done, Napoleon revealed his secret guard dogs (read: secret police squad), and Snowball was forced to flee.
At this there was a terrible baying sound outside, and nine enormous dogs wearing brass-studded collars came bounding into the barn. They dashed straight for Snowball, who only sprang from his place just in time to escape their snapping jaws. (Ch. 5)
While Snowball might have belonged to the upper class, he was not truly one of them. He felt for the little guy. He wanted to help the lower class. Most of the other pigs were not interested in this. Napoleon certainly was not. He was never a true Animalist. He saw the revolution as a way to get power for himself, not as a way to help his people.
This is common in revolutions, where the original idealists are mixed in with personalities who are just in it for their own power. Unfortunately, the people who have the pure motives are not always the ones who end up in charge. The lower class just exchanged one corrupt power for another corrupt power, and really things did not get any better for them.
In some ways, things got worse for the animals. They had less food and harsher lives, because they were working for a dream that never had a chance of coming true. They were forced to work for a dream fed to them by Napoleon, based on Snowball's vision. That is the worst betrayal of all.