I have no idea, but just check at the bottom of this page for the total amount of minutes played for each games (on PC only): http://www.xfire.com/
It gives you a good idea of how both franchises are doing in the PC world. =P
Personally, I want CoD: WaW to take it.
Random game thought :
Why is Bionic Commando Rearmed 2 getting so much hate? We finally get a real game and they're not even satisfied... I'm starting to hate the gaming community so f****** much...