Korra vs Aang, I think, would be less interesting. They have the same powers, the same elements, and almost the same martial art forms. They main difference is their mentality and body size. Mentally, Aang's against killing but isn't over incapacitating his foe, and Korra is too brash and obvious. Body is important; Aang would be more nimble and Korra more straitforward.
Korra vs Sora, however, would be more interesting. Sora has access to more 'magic' elements, some of which Korra can take advantage of, but Korra has generally better element usability. Sora's more used to wielding a blade, but the one you gave Korra is designed to draw blood, rather than a Keyblade's bludgeoning.