in discussing east egg and west egg, nick states that they are totally dissimilar. how do they differ?

From the text:

Twenty miles from the city a pair of enormous eggs, identical in contour and separated only by a courtesy bay, jut out into the most domesticated body of salt water in the Western hemisphere, the great wet barnyard of Long Island Sound. They are not perfect ovals — like the egg in the Columbus story, they are both crushed flat at the contact end — but their physical resemblance must be a source of perpetual confusion to the gulls that fly overhead. To the wingless a more arresting phenomenon is their dissimilarity in every particular except shape and size.

I lived at West Egg, the — well, the less fashionable of the two, though this is a most superficial tag to express the bizarre and not a little sinister contrast between them.

The West Egg is home to old money and respected names..... the difference between the two is social status rather than wealth.