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 clearly illustrates Sadie's optimistic and enthusiastic nature, while simultaneously showcasing Marco's skeptical and brooding disposition. Sadie's excitement about the concert contrasts sharply with Marco's pessimism, highlighting their differing perspectives and the dynamic of their friendship.