Castro vs Baez would have been a debate once, but not after Castro's September. No way Castro isn't in the lineup, although he might get removed for defense later in the game.
If Joe starts La Stella over Coghlan (which is really the only debate, I think), I'm guessing it's due to Joe's perception of La Stella's ability handle velocity. We've been hearing a lot about that lately. Probably it comes from Joe. I don't pretend to be able to judge Coghlan's ability against good heat, and I don't have access to the numbers (I expect they do). I think defensively it's mostly a wash. La Stella isn't that different from Bryant at third. Coghlan isn't that different from Bryant in the outfield (yeah, Coghlan is better this year, but it's only about six months ago he was collectively referred to as a butcher).
I already said I'd go with Coghlan for defense (and then I said it was mostly a wash, which I think it is). It's why I won't be surprised either way. If it's La Stella, bet it's about velocity.