The breed of goat should not impact its brush clearing ability. All goats will clear brush. They will also eat your shrubs and roses if they get a chance, which is why good fences are essential. What you want in a goat is more important here. Do you want big goats or little ones? Do you want to breed them? Do you want them for milk, meat or fiber as well as to clear brush? That said, if it were me, to just clear brush I would want a Boer or Boer cross because they are a little more mellow and easier to keep in as a rule than many of the other breeds.