Final answer:
The urban working class has historically had substantial influence on shaping popular culture, although the majority middle class tends to define societal norms. The upper class sets trends through their resources, but class traits are becoming less indicative of actual social class, allowing for a more complex interclass flow of cultural influence.
Step-by-step explanation:
The question of which class has the greatest influence on popular culture can be subjective, as influence can vary based on different aspects of culture and societal changes. However, historically and sociologically speaking, the urban working class has had a significant impact on shaping popular culture. This influence manifested through a festive public culture, as seen with the emergence of public figures like Phineas Taylor Barnum and the prominence of taverns as social hubs. Although they might not have the financial means to purchase consumer goods at the same rate as the middle class, the working class contributed to popular culture in meaningful ways, such as through music, fashion, and entertainment.
It is worth noting that while the upper class enjoys more power and control, and often sets trends because of their access to resources, it's the broader middle class that tends to define societal norms because they represent the majority. In the United States, the middle class encompasses a wide swath of the population, and therefore has a significant say in the consumption of goods, media, and entertainment, thus shaping popular culture.
The interclass flow of influence is also facilitated by the potential for social mobility, where individuals or groups can move between classes. The evolving nature of class traits, as they are less indicative of one's actual social class than in the past, further complicates the narrative. For example, a billionaire might dress in casual clothing, while someone from a lower income bracket may have luxury items.