The original and Reaper of Souls across all platforms
Diablo III has been performing rather well for Activision Blizzard. Since it released in 2010, Diablo III has sold over 20 million copies worldwide on all platforms. That's combined with Reaper of Souls too. Activision also stated that Reaper of Souls remained the #1 PC game in both North America and Europe.
I wonder if the upcoming PlayStation 4 and Xbox One releases of Diablo III: Ultimate Evil Edition will give this already amazing sales figure another significant push when it comes out later this month.