During the century it has become common, certainly amongst the BDSM community that a slave should be shaved, should have a chastity cage. This is a modern situation, it is often instigated at the Owner’s decision, but sometimes the slaves themselves choose to be body shaven and to wear a cage.
But in the olden days, such practice was not done. To be a real slave, in my view, is to be a natural slave. A slave would be bought at the auction or market looking like any free man would look like: hairy and penis on view and not caged.
I do like the look of a manly male slave: the pubes as they should be, the penis clearly visible so it can hang freely or be erect. As a naturist, and yes I am a nudist, but from a natural world perspective, a male is either naturally hairy or non-hairy or little hair. I would choose a male slave that does have the chest hair, that does have the pubes. But I would trim down a too hairy anal area!
To me there is no competition between the modern slave and the natural slave. My choice is for the natural slave. The natural slave is nude of course, as slaves should be, looking like a free male, but the only difference being the slave wears a collar, and is also branded as one. This is a good means to differentiate between a nudist Master and the slave.
I have not selected this picture because the penis is big but because of the hair that crowns the penis. Apart from the circumcised nature of the penis it is otherwise natural and is how a penis should look even on a slave.
I am sure others have their opinion on this, but this is my view which has come to fruition over time. Bearing in mind my naturist leanings: this penis underlines the natural look as nature intended.