tidus is definitely the leader if it wasnt for him yuna wouldve sacrificed her life and a guardians so the spiral continues he is the person that gives yuna the confidence to continue her pilgrimage

auron never did anything leadershiplike he was just an adviser leaders let the team have fun but know when to get to work they could have stayed at the moonflow for a couple of hours but auron advised them not to even though it wouldnt have hurt