The more I work with the Canon 5D Mark II the more I find myself using it as my primary camera, leaving the EOS1-D MKIII and EOS 1-Ds MKIII in my camera bag or even at home.
For sports, the 1D MKIII, with its fast autofocus and 10 frames-per-second shooting rate, is still my preferred tool but the 5D MK II becomes the camera of choice for assignments that don’t require fast autofocus or a high-speed firing rate. The images, in my opinion, are superior to the 1DS MKIII even though both have the same 21.1 megapixel sensor. The 5D has better firmware and superior processing of images through the Digic IV processor. The 1Ds MKIII’s dual Digic III processors is faster in processing but the 5D has better detail and less noise at high ISOs.
The EOS 1 series cameras are sturdier, better weather sealing, have a higher life expectancy for shutters and can handle two memory cards (1 CF and 1SD) and viewfinders that show 100 percent of the image but the image quality of the 5D, plus the lower price, makes it a better value.