Rule out the GM 6 cylinder engines. They had problems with the intake gasket (many failed multiple times over the life of only one engine) and some had problems with plastic parts used for coolant, and most have problems with EGR passages and valve, and the EVAP system valves once they get to around 115 K miles. I would rule them out of any engine that I would have chosen to have in a vehicle from the start and planning to keep it for 200 K miles or more if I knew then what I know now about them.