Something classical and clean, to provide a very visible contrast between what the battles are going to be portrayed in media to the public and how the battles actually unfold. I can almost guarantee the media will portray Leviathans and their captians much the same way it gave life to the pilots of WWI. Shiny, well-kept heroes that engage in gentlemanly combat in the skies above the normalfolk.
On the flipside, something to reflect the actual, inevitable horror of those battles, and of the factories that allow the battles to take place. Something dark and almost ugly as people die in horrible ways falling from the sky or burning in ammunition explosions or ripped limb from limb in deafening cannonades or crushed or maimed in some monstrous factory.
Vivaldi's Four Season fit the former perfectly, I think, especially Summer.
I can't really think of anything to fit the latter off-hand, sorry.
EDIT: Excuse me as I go try to cheer myself back up somehow.
