First I would like to clarify that I am neither atheist nor devout Christian. I am an agnotheist (I believe that there is supreme being but he is unknown). I met few friends online who claimed that they were atheist and this is what they told me: God is more wicked than Satan, Satan punished those who are sinners while God punished everyone even those people who have been good to him and spent their life worshipping Him.
I am not a literary expert, but between these two fictional characters, I would say the Christian God is more wicked.
God is like a CEO, Satan is just a regional branch manager, appointed by God.
God organized his business and is ultimately responsible for all the wickedness in the Christian story.