Who killed more people Atheists or Christians?

[Fidel_Castronaut]

Christians kill in the name of christianity.
Atheists don't kill in the name of atheism.

For example the Ustase.

http://en.wikipedia.org/wiki/Usta%C5%A1e

The Ustaše intended to create an ethnically "pure" Croatia, and saw the Serbs that lived in Croatia, Bosnia and Herzegovina as their biggest obstacle. Thus, Ustaše ministers Mile Budak, Mirko Puk, and Milovan Žanić declared in May 1941 that the goal of the new Ustaše policy was an ethnically clean Croatia. The strategy to achieve their goal:[66][67]
One third of the Serbs were to be killed
One third of the Serbs were to be expelled (ethnically cleansed)
One third of the Serbs were to be forcibly converted to Catholicism

See the bold this was deffo a religious persecution on the part of the croats.

And of course throughout its history chrsitianity has persecuted the jews, with one inventive English sailor during Edward the firsts reign charging the jews for passage away from England and dumping them in tidal spur halfway between England and France then inviting them to swim the rest of the way. Jews didn't return to England until Oliver Cromwell invited them back in.
Then you have all the many and disparate sects of christianity fighting against their big rivals, other sects of christianity going back to the Goths during the roman empire, Perseution of witches and anyone else they didn't like at the time and you end up with a religion which looks a lot like the intolerant blood dripped religion that Islam looks like now.

Fun fact. The Ustase were probably the most brutal regime to be seen during the entire Second World War (and that's saying something). They were also whole heartedly supported by the Vatican at the time.