Here are four core arguments against God's existence that have persisted since ancient times. Using these four arguments as an organizing principle, I present for your consideration the Four Horsemen of 1854-1900.
The argument from inconsistent revelations- Sectarian religions are mutually contradictory and internally inconsistent. Mark Twain observed that the religious will cherry-pick indefinitely rather than abandon the notion of divine revelation altogether.
Lack of empirical evidence- Discovery trumps revelation. This is the skeptical or naturalistic argument. As Friedrich Nietzche suggested, faith is a form of collective insanity.
The argument from reasonable nonbelief- If the existence of the gods were self-evident, everyone would believe. The burden of proof is on religion. As Oscar Wilde observed, faith is not a virtue.