Taysom is awesome, but Tanner is also really good. Taysom is a better athlete, but Utah's front-7 is athletic enough (At least in comparison to BYU's O-Line) that it may be a better matchup for Utah to play Taysom than to play Tanner who tends to release the ball a little bit quicker.
A part of me prefers that BYU play Taysom to avoid Tanner getting another year of reps to develop. Assuming he continues to improve (And doesn't have a Heaps-like sophomore slump), Tanner is going to be a very dangerous QB his Jr and Sr seasons.
Plus, I want to see if all the CB claims are true that having Taysom in the game is basically a +35 point difference than BYU without Taysom in the game. If true, BYU should definitely go undefeated next year.