Noise, ISO 1600, D5100 vs. T3i

Canon leans just a touch more on the color noise suppression than Nikon, which I think produces slightly better results. It also helps that at equal settings, the T3i delivers brighter exposures, with slightly better white balance, than the D5100.

(1/30 sec, f3.5, AWB, ISO 1600, default color styles)