That's the crux of the entire argument--is Taysom the better QB? If so, he should start. I know many believe Taysom is clearly better than Tanner, but I feel persuaded by the fact that Taysom struggles to stay healthy, that Tanner performed so well with very little preparation, and that Tanner will probably fit TD's system better.
I could be completely wrong, but I don't think either side can say that Taysom is clearly better because we don't know what Tanner will look like after a full year of preparation.