The Coolpix S31 has a CCD sensor type which is better than the MOS sensor type found on most digital cameras that have been available for more than two years. CCD sensors produce high quality, low-noise images but consume a lot more power than CMOS sensors. CCD is the most common image sensor type used in digital cameras.
A CCD sensor type is in fact the best sensor type amongst all digital cameras of a similar spec and age to the Coolpix S31.
The worst sensor type across similar types of digital camera is MOS.