Ginny and Demelza
Sorry Demelza, but Ginny would probably not be a very good partner. Very much like Neville, she would focus on blocking the spells being thrown at her and not really using anything offensive -- unless it's something minor like a stunner. She wouldn't be out to hurt Demelza at all, and DEFINITELY wouldn't use any of the hexes or curses being taught by Amycus.