Of the three main diesel motor suppliers, Cat and Cummins are the two best. Navistar (IH) has had a lot of issues over the years with motor technology. And I believe I read a while back that Cat no longer produces on road motors. The I6 Cummins is a proven motor with millions and millions of miles to its credit. But to be honest, if I were looking for a MH today motor choice would be low on my priority list of things. As long as it had enough power to move me down the road at a comfortable speed thats good enough.