How to compare CMSs, objectively

There are literally hundreds of CMSs on the market, possibly thousands. So much choice, but often so little satisfaction, judging by the gripes of end-users. Why is the right option so muddled? Old CMS vendors soldier on, and new ones enter the market all the time, promising a better future. How do we make sense of this? A large part of the answer is the CMS buyer, and CMS users, are different people. The buyer and user have completely different relationships to the CMS.