Do Americans aspire to be altruistic or selfish?

Ayn Rand's book Atlas shrugged is apparently the second most influential book in the USA behind the Bible. Unlike the Bible which many claim advocates charity and altruism, Ayn Rand's philosophy promotes selfishness and pursuit of one's own happiness as the purpose of life. So with such different philosophies how can these two books be the two most influential books in the USA, unless one is for the monied elites and the other for the masses. What do you think?