Question

So we just started reading Beowulf at school and we're around ch 8. Our question to answer was Whose account of Beowulf and Brecca's swimming match is more credible/believable and why? This is referring to Unferth's and Beowulf's stories. I said that Beowulf had the believable account but I actually don't have good supports. Can't someone help me find specific supports from the book?