Although it's a nice idea, in reality such a comparison wouldn't really be practical. I don't know of any devices that are able to capture in raw, DV and MPEG-2, and if you use different devices for comparison then the result might be influenced by the performance of the hardware itself rather than the compression.

A suitable demonstration I suppose would be to capture uncompressed using a PCI capture card, and then encode the same uncompressed source to various different formats.

I might have a go at this in the futurer. The MPEG-2 encodes would obviously have to be CBR.

PNG (lossless) would be the best format for screenshots.