The dialogue that best helps develop both characters for readers is:
“No way!” Sadie beamed. “Clear your schedule. We’re going to have a blast.”
“I don’t know,” Marco said slowly. “Are you sure we’ll even get tickets? This is going to be a pretty big deal.”
This option effectively showcases Sadie's optimistic nature through her excitement and determination to have a good time. In contrast, Marco's response highlights his skeptical outlook, reflecting his tendency to doubt good luck and focus on potential obstacles. Their contrasting perspectives on the situation are clearly established, emphasizing the dynamic of their friendship.