I'd still have to say.. Nothing, dur-duh-dur!!
If nothing existed there cant in any way shape form color place and language be something there unless you're talking about an empty space or a paradox or simply an empty void, but if nothing existed.. Those wouldn't either.
And the people talking about the definition of nothing..
If we never existed and same as everything else, then the word nothing wouldn't exist nor have a definition.
And no offence to any religious beliefs, god isn't proven to really exist. You cant see or touch it either so you cant know it's there. And if nothing is there, the belief of god wouldn't exist either. Fact or fiction wouldn't exist and nor would religion. If nothing existed, the spiritual plain wouldn't exist either. Just looking at the scientific view of it, no offence.