They all have problems. The Cummins is hamstrung by the poorly designed "truck" built around it. The Dodge's firewall wraps around the Cummins, and comes too close to the #5 & 6 cylinders, restricting airflow around the back of the engine, causing theses 2 cylinders to overheat, leading to piston galling. Most of the Cummins in the late model Dodges melt one or both of these pistons when they fail.
Fords 6.0 Navistar VT365 engines suffered from being rushed into the market before they were ready. The fuel systems were especially inadequate, and the turbos are too complicated for their own good. The engines are also prone to overheating, and if you do overheat one, you're stuck buying new factory heads if you warp your originals, which you will. These are expensive engines to fix.
Duramax suffers from a lot of the same problems as the 6.0L Ford. Most of the dead ones We see die because of abuse, they are a powerful engine, and many people can't seem to keep from beating the snot out of them. This is another terribly expensive engine to fix, and once again, the heads aren't generally reusable.
I sell diesel engines, and diesel engine parts, 60 hours a week. Every friggin' week. My customers are some of the most noted diesel shops in the nation. My conclusion after 20 years of this crap? Give me a late '90s Ford chassis, with a mechanical 5.9 Cummins, and a manual transmission. I'd take a 7.3 if necessary, but the 5.9 is cheaper to maintain. And I detest electronic injectors!
