What's the strongest argument for atheism?

Energy is a form.

Dark matter is formless.

dark matter is nearly but not completely undetectable

the form that we are able to detect is rather like a large blob, based on its gravitational signature

Energy is a form.

Dark matter is formless.

there is no such thing as form without matter

there is no such thing as matter without form

Atheism is another religion

What is the form of an electron, is it in the form of a particle or a wave?

I myself am religious, but my best argument for atheism is that science is always progressing, and therefore the unknown about the universe may soon be known and explained by science.

So you are making a claim that matter exists.

The burden of proof is on the one making the claim, prove the existence of matter.

That is why I do not adhere to the philosophy that only things that are observable can be known with certitude.

only what is logically-necessary can be "known with certitude"

But if that is the philosophy you adhere to, fine! I dont think it answers all questions and it certainly limits knowledge.

I do not find that intellectually honest. Why cant I have certitude about a perfectly logical and consistent argument?

So you are making a claim that matter exists.

The burden of proof is on the one making the claim, prove the existence of matter.

the keyboard you are typing on qualifies as undeniable and conclusive proof

What is the form of an electron, is it in the form of a particle or a wave?

an electron exhibits both particle and wave properties, a concept known as wave-particle duality

an electron has mass

"particle" is a form

"wave" is a form

the keyboard you are typing on qualifies as undeniable and conclusive proof

Restating your faith-based assumption and saying it qualifies as undeniable and conclusive proof of your faith-based assumption isn't a proof by any stretch of the imagination. Besides just proclaiming that your faith qualifies as proof, do you actually have an argument?

You said you were a monist, you supposedly don't believe in duality. 

Particle and wave are mutually exclusive forms.

Temporally speaking, a wavehas a periodicity, and spatially, it is spread out in space, a particle cannothave a periodicity, nor can it be spread out in space. A particle has adiscrete location in time and space, a wave does not, a wave spread out over alarger region of space and time. A wave has amplitude and a frequency, itexhibits the phenomena of diffraction and diffusion, a particle does not. 

So you must think Math is a religion.

Do atheists believe the God in what's called the bible does not exist?

Actually, atheists know that the God in what's called the bible does not exist.