Hi Moazam, I'm not sure how much difference there is between them in low light/ISO/noise.
Re using the in camera crop mode, apart from saving on memory/processing, I don't think it helps with images.
I find cropping in on the computer afterwards gives the same sharpness/clarity/detail (I use a D800)
tbh I find it better not using it, because I have more leeway to re-compose the image afterwards if I need/want to.
btw,He who dies with the most toys, WINS!Nikon D800E & D700 bodies + Nikon 200-400mm F4 VR1, 50mm F1.4G, 16-35mm f/4G VR, 105 F2.8 VR macro, 70-300mm lenses. A couple of filters, Giotto tripod & ballhead. Lowepro Slingshot 302 AW