2013 Taysom had a full season and only won 8 games as a Sophmore. He has looked great in both 2014 and 2015 and likely would have had elite seasons in one or both of those, but the dude just can't stay healthy. Tanner won 9 games as a Freshman and was thrown into the starting role less than 3 months removed from his mission. And he delivered some of the most excited moments I've experienced as a BYU fan. He is a great QB in the making.
I just don't think anyone knows who is BETTER yet, maybe not even Detmer, because Taysom is still not 100% and no starter has been named. We will know more in fall camp. Until then both QB's should be considered equal and given the same opportunities.