Keep them all. These things have a way of working themselves out, and being arrogant enough to think you can outguess random chance is how we wound up where we are right now not just with real holes on the team, but also with a lot of mediocre patch players like Aviles and Salty playing as well.
To call a position secure for the future, you need three prospects potentially ready to play it in the next 36 months or less. Any time you move prospects to "clear the way" because one particular player is "your guy," especially before "your guy" has demonstrated over a full 162, you're inviting catastrophe. That "clear way" becomes a hole in a real hurry at that point.
In other words, trying to chose, say, Ellsbury over Bradley, reveals your blindness to the fact that in the uncertainty-filled world of prospects and young ballplayers, we are very very likely to find a place for both over the course of 162+. Exactly the same way we could really have used Reddick this year, and DID make good use of him last year, despite him not being in the plans at the outset.