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 effectively showcases Sadie's optimistic nature and excitement about the concert, while Marco's skeptical response highlights his brooding character and tendency to focus on the negative. This contrast between their personalities is clearly illustrated in their differing perspectives on the event.