Comparing East Egg and West Egg, it's just two different classes of wealth. One is new wealth and the other is old wealth. West Egg being the one with the new wealth, the ones who just became rich. This is the category Gatsby himself falls under, as he throws lavish parties to impress. The difference is that the people in East Egg are used to the money, they are all born into rich, while on the West Egg you have to work hard and find your way to the top.
East Egg is the area of the Island where the rich people with old money live. In contrast the West Egg is the area of the Island in which the new money live. People who have just come across their fortune and are looking for ways to move up in society.