The kidneys receive about 25% of the total cardiac output, which I believe is the largest proportion going to any one organ.
The liver receives a large part of its blood supply from the portal vein, which is not considered to be part of the cardiac output, and therefore may receive a larger total blood supply while receiving a smaller percentage of the cardiac output than the kidneys.
I don't remember ever hearing that the brain receives a greater blood supply than the liver or kidneys in normal physiology, but in a hypovolemic state (esp in shock) the blood flow to the brain will be preserved at the expense of other organs- such as the liver and kidneys- and in this state could be said to receive the greatest blood supply.
Does that make sense?