Tough question.
My vote goes to Galliano. It's REALLY tough having to choose between these two. But I feel Galliano paved the way for theatricality becoming apart of fashion's identity in the 2000s. From there, as Galliano began to slow down with his collections- McQueen began to grow and sort of took that idea of theatricality, pushed it into obscurity, bizarre imagination, took ownership of it and bolted off!
But honestly, with what has happened towards the end of their careers- it's hard to say whether or not this is a fair poll (ideally, it'd be their best collections versing each other).
Either way, you can't go wrong with either choice.