I would think it would be the two heifers followed by the dry cow then the bull. Bulls very quickly become lazy old mongrels that just want to lie down and sleep unless they have a cow to follow. This is just my opinion, nothing proven but I don't manage pasture by either, I manage it by looking and seeing what effect the cattle on it are having so I can move them on if necessary. I guess I use numbers to some degree deciding how many cattle I can keep. I have my bush block which is my buffer where I can put them when the pasture is getting too much pressure until things become more favorable.
Ken