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 highlights Sadie's optimistic nature as she enthusiastically imagines the fun they will have, while Marco's response showcases his brooding skepticism about the situation. It effectively contrasts their personalities and sets the stage for their dynamic as best friends.