The dialogue that best helps develop both characters for readers is:
“We’re going to have so much fun,” Sadie said. “I bet we’ll get to meet the band. I bet we’ll even get to hang out with them!”
“We probably won’t even get to go,” Marco said. “I bet the whole show will get canceled and we’ll have a terrible day.”
This exchange showcases Sadie's optimistic nature as she enthusiastically imagines all the fun possibilities, while Marco's skeptical character is highlighted by his pessimistic outlook and focus on potential negative outcomes. This contrast effectively illustrates their distinct personalities.