The strongest argument for Atheism is emotional and physical pain. That if God truly existed 'physical evil' such as killer storms, earthquakes, etc., would not exist. Our loved ones would never get sick and die. No one would get killed and eaten by any animal or reptile. Spiders and snakes, and Komodo dragons would not catch, kill, and eat their prey like they do. Theses things are horrible to us humans. Therefore, since these things exist, and people seem to die and/or be injured so randomly, God does not exist.
This is not my belief, but the Atheistic belief.