Originally posted by jpzk I mean, what's better: a sensor with 24 MP with "small" photosites or a "16 MP" sensor with larger photosites?
Everything else being equal (quantum efficiency, read-out noise, etc), they are equal and the 24MP sensor has the advantages
listed by Jay.
A 16MP crop from a 24MP sensor, e.g., taken to increase "reach", won't have the same quality as a non-cropped shot from the 16MP sensor, though. The reason is that you are not using the full surface of the sensor and increase enlargement which will show more noise.
A 16MP crop from a 36MP full-frame (Nikon D800), on the other hand, will have the same quality as a non-cropped 16MP shot from the K-5.