Right now the best argument for atheism comes from the crazy religionists. I posted a Doonesbury cartoon and in case you missed it I will post it again.

All of them

All of the above, and Matt Dillahunty and Tracie Harris from the Atheist Experience. What I love about Matt is he points out how ridiculous some theists are about their fairy tales.

Since an atheist rejects by definition, what is there to 'argue for'? We aren't monolithic; only sharing one element of our many, varied complete descriptions.

Attempts by Dawkins', Harris' et al, to confine us within criteria for qualification that they deign to issue on our behalf is pure Popery. It belongs to the mentality of theological clerical hierarchies.

So-called atheist leaders definitely argue for. They argue for establishment of doctrines governing just who is and is not a true Atheist. The Judas Goats never rest.

What do you mean by best? Are you asking which advocate is the most effective?

Different strokes for different folks. I like them all but Dawkins holds a special place in my life.