Both pitchers are ridiculously similar, and I don't think you can go wrong with either. Gray's off-speed pitches are better, but his fastball results aren't great. In particular, he walks more than he K's with the fastball. Stroman's results (while fairly sss), are much more consistent across all the pitches except his changeup, which he doesn't use much. That gives him more ways to get guys out, and I would think should result in better performances in the long run.