Forgetting considerations such as player development, egos, and money, what is the 25 man roster you want to see the Red Sox run out there?

I assume you mean "of available talent". Otherwise A-Rod would be the starting shortstop.

Lowrie > Cora
Kielty or Moss > Thurston

...and that's about all I'd do for the roster.

On player development, I can separate the notion of "he might benefit from regular use as a starter in the minors" from "he might not yet be mentally/emotionally ready for an MLB role". They're both player development issues, but for this exercise I can only ignore the former. The former affects how ready he'll be in the future, but the latter might also affect his performance NOW, which I think is the point of the exercise. As such I'm not interested in using someone like, say, Masterson in place of Timlin, Aardsma, or Lopez.

vi,
You were correct with the assumptions.

I would like Moss over Casey, Lowrie over Lowell, Hansen over Timlin, Corey over Lopez, and Brown over Cash.

Lowrie over Lowell...that's bold.

I meant cora. sorry