For the vast majority of DSLR shooters these cameras are a lot of money so it is important to get the right one. Often it could be a small feature that sways it for your individual needs so it is never right to say that one camera is ‘better’ for ‘everyone’. It isn’t as cut and dry.
However it is possible to be objective about image quality. I’d say the 5D Mark III definitely has the better internal codec and resolution.