You forgot Cadmium, Lithium, etc Bromide I believe that the choice of bromide somewhat influences the lifespan and contrast of the emulsion this is at least the case in the wetplate world. Cadmium was the preferred Bromide because of the keeping qualities of the emulsions. Ammonium ads a little speed but lowers the lifespan of the emulsion. Sodium and Potassium Bromide should be about equal at least according to older literature. It's also important to know where the formulas were created for example German formulas (Agfa) liked their potassium bromide because it was readily available. Economy does play a role in the choice of ingredients.