I would have said Goofy if this were KH 1, but he had a lot of new abilities in KH2 that makes him more valuable to the team than in the previous game. So I say both of them were very important for their specific powers. Goofy had knocksmash (take that Demyx >_>) and Donald is a great healer. He's always there when I need him. You really can't go wrong with these two.