It would really depend on the type of atheist. If they were just your typical atheist, then I would have to find out more information on the two candidates to see who had more skill. If they were like the Atheists on this site showing a lack of reasoning and coping skills, I would go with the Christian.
But if we walk in the light, as He is in the light, we have fellowship with one another, and the blood of Jesus, His Son, purifies us from all sin.