So either 6-3 with a guaranteed loss to ASU or 6-3 with a guaranteed loss to BYU? Then I take BYU because it's one more win.
Are you saying I can choose between 6-3 but losing to BYU OR 5-4 but beating BYU? Then I probably take 6-3, because that's sometimes enough to win the South (it was in 2018, in 2015, in 2012, and 2011)