What sort of images produce least noise?
There are basically two ways to approach this. In both cases what you are doing is increasing the amount of total light that enters the camera so that the random nature of photon shot noise is minimized by the increased amount of total data (photons striking pixel wells).
- Long exposure images shot at lower ISO when combined with in camera dark frame subtraction.
- Stacked multiple exposures shot at higher ISO settings that usually use a dark frame shot at the end to subtract read noise caused by sensor heating.
In both cases, you are either shooting static scenes that don't change for extended amounts of time or you are allowing the blur from moving objects to be incorporated into the photo.
If you're shooting in low light, the noise is mostly caused by the randomness of the number of photons hitting each sensor sight. So in one sense what you're shooting doesn't matter. But... you can reduce the noise a good deal if you take multiple exposures of the same scene and then stack and average them in post-processing. So my answer is a static subject shot on a tripod.