I'd take Greinke/Gallardo.
Heads of state that ride and wrangle. That look at your face from more than one angle. Can cut you from their bloated budgets. Like sharpened knives through Chicken McNuggets.
If we're taking contract situation into account, then I'd prefer Latos and Cueto. If we're just talking about ability, I'd take Greinke and Gallardo since I don't really trust Cueto to reproduce last year's results and I think he'll continue to have some durability issues due to his small frame.
But consider last year. You would not have even considered this a serious question with Volquez/Wood starting games 1 and 2.