There are trade offs to be considered when selecting meat for the feast. Human fat is high in cholesterol. But, it makes the meat juicy and adds flavor. It like selecting a piece of beef. A well marbled prime rib is preferable to lean one.
The entree from the athletic body has less fat and is lower in calories. But, the meat can be tough and dry. It should be marinated overnight before cooking and you need to be very careful not to over cook it.
From what I understand about cannibalism, the whole human on a spit over a fire is a stereotype created for movies. You can not cook one part of the human properly without overcooking the other. They also have to be properly gutted, cleaned and dressed like any other game animal you might eat. Most cannibals only eat certain parts of the human such as the genitals which are considered to contain a man's power. Thus, the consumer supposedly acquires that power.
Most of the time, cannibals boil human meat to make it tender. Maybe they add Old Bay Seasoning to the water for flavor.