Camera Meter Exposure
I think the properly expose picture gives the best exposure because since she is wearing white on a white background, the properly expose image is the one that gives the best contrast between her and the background.
Well Expose Image
100% - Well expose picture
100% - Underexpose picture
The underexpose picture has the noise worse mainly because since it's darker, we can more of the noise.
The JPG image was developed in the camera so the picture has more contrast, for example. Before turning the photographs in black and white, the JPG also had more saturation,