Also note that if you get the camera to do the NR...it drains your battery too....so you want to save as much power as possible especially if all you have is one battery, features like this and others should be turned off. There are s/w that can do the noise reduction for you more effectively offline on your PC or Mac
As of other settings, I prefer doing the noise processing by myself than to let the camera handle it. Some process the chrominance noise selectively and leave the luminance noise untouched, and some critical users might have a slight change in color. I usually manage them individually for different shots.