....tongue in cheek friends....
Good slaves? Realistically? .. how about breeding a group of people (mainly men with superb technical skills and a knack for understanding history and other esoteric subjects) that will spend copious amounts of money each month on rulebooks of diminishing quality and/or power-creeping feats/skill tricks/what-have-ye?
Another good slave would be someone who takes the time to weigh individual boxes of 'War of the Dragon Queen' in the vain hopes of getting his (less likely her) dreamed of Huge mini.
And let's not forget the upcoming master: 4th edition.
C.I.D.