none of the above

I've never seen any definition of "atheist" from any respectable source that required absolute belief that there was no God.

Usually the only time agnostics use that argument is when they want to claim that they are intellectually superior. They never come up with any basis other than their own opinion which seems rather too obviously self-serving.Of course it may be that they tend to the view that God doesn't exist but aren't happy with the idea of calling themselves atheists. So far as I am concerned I don't mind what they call themselves but that doesn't give them the right to dictate English usage.

And like I said it doesn't say anything about absolute CERTAINTY that there are no Gods.So far I've been sticking with "atheist" or "agnostic" as they are used in ordinary speech, but the fact is that there are other usages and "agnosticism" is often classed as a form of "atheism". (For instance "agnosticism" is explicitly listed as one of the definitions of "atheism" in _The Penguin Dictionary of Religions_).