i have a thread dedicated to this here.
http://www.vgchartz.com/forum/thread.php?id=88468
I am using VGC, firstly cuz we r discussin gon vgc n it doesnt seem right to use some other numbers n secondly n more importantly the admins of VGC r not afraid to adjust numbers if they r wrong.. after all they r not covering 100% market.. so i like it that they update number when some new information from reliable source is available.. So i dont think this difference will remain when the next week numbers will be published.. n correct adjustment will be made.