Is Manabu better at socializing than Suzune?
Manabu criticized Suzune for being so aloof with her classmates in Year 1 and told her that isolating herself wasn't going to help her reach Class A. He also seems to be on much more friendly terms with his classmates than his younger sister is with her's. Even students from outside his grade/year will usually say good things about him, implying that either he has made a good first impression on those students or those students have heard good things about him from others.
Though there is a statement from Tachibana that kind of contradicts this. IIRC, she says that he mostly achieves victory for his class all by himself and that sometimes their classmates somehow hold him back or smth. This implies that Manabu's relationship with his classmates might not be all sunshine & rainbows unfortunately.