One of the important things that Snowball brought to the farm, and that his character shared with Leon Trotsky, was a genuine desire to improve life for the every-day person. It was what got Trotsky chased out of power in Russia and what got Snowball chased off the farm.
Snowball was also very curious and enterprising, following rational principles in terms of trying to improve the lot of the animals. Whether it was designing the windmill or working to find ways of getting more out of the work they did, he had a very sincere interest in helping the animals rather than elevating himself as Napoleon did.
Snowball seemed to be more of an animal of the people (or would that be pig of the animals?) than Napoleon. He worked with the other animals trying to educate them; he proposed the windmill to provide energy for the luxuries and by-products that the animals desired; and he organized and led the first battle with the humans. He was less ruthless and deceitful than Napoleon, and Snowball would probably have been satisfied with far less of the human luxuries of the house that so enraptured Napoleon. His superior intelligence would probably have figured out that Frederick was out to cheat him and the botched deal for the firewood would have been averted. Snowball would have likely avoided the human traits that Napoleon eventually accepted. Although the farm may not have been as financially successful under Snowball, the animals themselves would have had a better life.
To me, the only indications seem to show that Snowball would have been at least somwhat better than Napoleon if he had been who became leader of Animal Farm.
First of all, I think we can see this because Napoleon is the one who is shown doing the "bad" stuff, even before he expels Snowball. Napoleon is the one who takes the milk for the pigs. Napoleon is the one who takes the 9 puppies and trains them to be his enforcers. Snowball does not do anything like this.
Second, Snowball seems to work hard for the sake of the farm. He is constantly reading and trying to figure out ways to improve things (windmill, learning how to run a battle). This seems to show that he is more interested in actually helping the animals more than he is interested in getting power.