Okay, to begin with let me just say that it's difficult to seriously answer this question without coming across as just plain creepy and ghoulish. However, as I would hope to find good feedback on a difficult question, I'll offer my opinion with the one proviso that no one think me a freak for putting this much serious thought into this topic. I will do my best here to answer as clinically as I can as someone who enjoys eating and cooking meat.
For starters, the direct answer to your question, the secret to a good cut of meat is all about marbling and texture. It's true for beef, pork chicken and any other meat source I know of so I imagine it's the same for a human body. Marbling, simply put is the ratio of fat to muscle. Also important is the density of that muscle.
Muscle is what we carnivores most like to eat, but the trick to cooking it sufficiently is that you have to trap in the moisture that's in the meat. Marbling helps with this because of it's oil content. It forms a natural barrier around the muscle, ensuring that the moisture is kept in the muscle which keeps that tissue from becoming too tough.
Good examples of tissue on a human body that would feature these characteristics would be buttocks, back muscle tissue, upper arms, shoulders, breasts, abdominal muscles and thighs.
For the record I am aware that a woman's breasts are mostly fatty tissue, I'm referring to the actual muscle tissue more visible on a male body.
Now this is where this question gets really creepy. I get from your question that the cannibal or cannibals in your story aren't necessarily doing this for the nutritional value of the meat. Instead they seem to be doing this for fun. I would imagine that this would play into their preference for the cut of person meat they're interested in.
Keep in mind, to resort in cannibalism a person must be either desperate for anything to eat or completely screwed up in the head. When I think screwed up in the head I realize that the vast majority of people who fit the screwed in the head category that I have met demonstrated sexually deviant behavior and that somehow sex was linked to at least the outward manifestations of their mental illness.
The point I'm trying to avoid making here is that you shouldn't discount the erogenous zones on a persons body when contemplating what a choice cut of meat would be. Perhaps these areas may not provide the best meat or the most nutritional value, but they would appeal to a person who was engaging in this behavior for any form of pleasure.
please, again I say, I'm only offering ideas here because I can appreciate that this writer is approaching a difficult topic and would like to offer feedback. I'm not seriously discussing the consumption of a human body as something that I find the least bit interesting.
