Which H!kagero should i build?

ATK is only stat that matters. -DEF +SPD is bad but better than -ATK.

-atk +HP for enemy phase builds because you don't want to lose her def and the bonfire/iceberg will destroy most things. Same logic could potentially apply to player phase builds, but on player phase I'm less wary of losing her def so I'm more willing to keep atk over def.