Good question. Cozart was two and a half years older in Dayton in 2008 than Rojas was in Dayton in 2009. Both Cozart and Rojas were exceptional defensively in Dayton. I don't think you could clearly place one above the other. However, I was told that Cozart regressed a bit this season in Carolina (he had 23 errors after having 10 in 2008 in Dayton in a little less than a full season). The Cozart I saw was very good, the best in the league. Rojas was also the best in the league and finished with 13 errors in a full season. Neither has an exceptionally strong arm. Both are extemely smooth and consistent. Rojas is a bit flashier. If you asked me to pick between the two, it would be a tough call, but I might have to give a very slight edge to Rojas, just because of the age difference and he is still improving rapidly.

I think most would tell you that as of this moment, Janish is ahead of either of those guys defensively, which is more a credit to Janish than anything against Cozart or Rojas.
Agree that this was a great question from mace. Nothing wrong with having a few major league quality gloves coming up at the SS position. Rojas improved offensively quite a bit in the 2nd half. Do you see any hope for him as a hitter?

My take on Janish is that what separates him is the arm, which looks elite to me. I doubt there are any shortstops in the majors whose arm you could definitively say is stronger.