Honestly, D5100 is far better than Nikon D3100, both in terms of sensor technology and advanced features. The Nikon D3100 has a 14.2-megapixel sensor, which is relatively less than the 16.2 megapixels of the Nikon D5100. Additionally, the dynamic range and ISO range of Nikon D5100 are also relatively better. Plus, the screen resolution is also highly impressive.