According to the results, Nikon D3100 is slightly better than its competitor Canon 550D but still behind Nikon D5000 and Nikon D90 score. DxOMark is a comprehensive RAW-based image quality Measurement Database and a set of Scores to evaluate and compare digital cameras and lenses. It is open , industry-standard and performed by indenpendent people using state-of-the-art equipment .

Check the full comparisons below :
Nikon D3100 vs D5000 vs D90
Nikon D3100 vs Canon 550D vs Nikon D3000