Breeders- can improve stock toward existing breed and variety standards , sometimes creating new ones
Reproducers- buy good stock, can raise some nice birds, but often have to go back to the breeder to keep getting stock in order to maintaint quality
Propagators- hatch birds of questionable...
What makes a good breeder? I kind of equate it with the old saying about a good coach " he could come into town and beat your team, then turn around, take your team and beat his". In other words give a group of people each a similar quality trio of birds, in say five years the good breeders...