We have used Optimus Prime and he seems to work on just about everything. They mature a little early so a big framed later maturing cow would be best. I have not seen a bad Optimus Prime calf yet. Our herd bull this summer was an OP son and he was great. They have excellent dispositions. They have all been deep and thick and sound. A couple we had out of a Who Da Man were a little weak just behind the shoulders, but grew out of it. Haven't used Momma's Boy, but have seen a couple of calves, that were really good. Dunk's Lucy was flushed to him and those calves were very consistent and good.