Overdrive on or off?

Generally automatic transmissions are programmed to shift based on load and RPM, the engineers that develop these shift points know what there doing, what they don't know it the environment your engine is running in. One thing I do know for a fact is if a transmission is shifting constantly it is building heat, and wear and that is not a good thing. For me I want my transmission to keep my engine close to it's peak torque curve, that is going to put the least amount of strain on the engine and produce close to the best fuel mileage.
A standard transmission normally doesn't care how many times it is shifted as long as the driver isn't banging gears. Some drivers do have a tendency to lug an engine that is backed by a standard trans.