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 highlights Sadie's optimistic nature and Marco's skeptical demeanor. Sadie's excitement and belief in a positive outcome contrasts sharply with Marco's pessimism, giving readers a clear understanding of their personalities and how they interact with one another.