@tyrone_40
Dear sir, its simple.
Keeping all the maintenance related issues such as changing of oil, etc constant, an automatic car has a better chance of having a better engine.
It is due to the fact that the clutch and gear are controlled by the car itself depending on the speed, load and the level of throttle. The car changes into next or down gear depending on its calculations. The driver can therefore never overrev the engine or run at lower speeds for higher gears. Following example would explain it better.
In a manual car, a person can take his car to the maximum speed possible in a single gear, let's says 2nd or third. he would not change his car to next gear even on a high speed such as 100 KMPH. This gear is too low for this speed and the engine will be revving at very high speed. This may damage the engine.
In an automatic car, this will not happen as the car will automatically change the gear. There is a limit to revving of engine and most automatic cars do allow for higher revving but only to an extent.
If there is any more query, please fell free to ask.
Regards,