How are Snowball and Napoleon different in Animal Farm?

Snowball is more interested in having all animals collectively maintain the farm and benefit from it, while Napoleon just wants power. 

From the beginning, Napoleon is scheming and Snowball seems clueless about it.  Snowball seems to have bought in to Old Major’s vision of the farm, and is trying to make it happen.  Napoleon, on the other hand, does nothing but create division and try to benefit himself. 

Snowball also busied himself with organising the...

Snowball is more interested in having all animals collectively maintain the farm and benefit from it, while Napoleon just wants power. 

From the beginning, Napoleon is scheming and Snowball seems clueless about it.  Snowball seems to have bought in to Old Major’s vision of the farm, and is trying to make it happen.  Napoleon, on the other hand, does nothing but create division and try to benefit himself. 

Snowball also busied himself with organising the other animals into what he called Animal Committees. ... On the whole, these projects were a failure. The attempt to tame the wild creatures, for instance, broke down almost immediately. (Ch. 3) 

Snowball wanted to get all of the animals educated. He succeeded in getting the pigs to read, and some of the other animals learned to read or learned the alphabet.  The animals become divided on whether they agree with Snowball’s plans to build the windmill or Napoleon’s idea that it is a waste of time and effort. 

Snowball and Napoleon become increasingly at odds.  Eventually, Snowball can’t even make a speech without the sheep blurting out “Four legs good, two legs bad” to interrupt him.  Napoleon and Squealer support them doing this. 

Napoleon takes the puppies and trains them secretly to be his guard dog force.  He uses them to run Snowball off, and then uses Snowball as a scapegoat for everything.  Snowball never saw it coming.  Napoleon goes from opposing the windmill to announcing it will be built. 

On the third Sunday after Snowball's expulsion, the animals were somewhat surprised to hear Napoleon announce that the windmill was to be built after all. He did not give any reason for having changed his mind, but merely warned the animals that this extra task would mean very hard work, it might even be necessary to reduce their rations. (Ch. 5) 

Squealer, Napoleon’s mouthpiece, tells the animals that Napoleon was never opposed to the windmill.  Snowball was a traitor, working with Jones.  If the animals do not work hard, Jones will come back.

In short, Snowball is idealistic and cares about all of the animals.  Both Napoleon and Snowball are ambitious, but Napoleon's ambition is directed at getting power for himself.  He knows how to use other animals, such as Squealer and the puppies, to make that happen.