[Hi Ho]

It's hard to put a number on it but because composite (single RCA connector) mixes everytyhing into one wire it has the lowest quality. S-Video seperates the signal into chromanance (color) and luminance which increases the quality a bit. Component (3 RCA connectors) seperates the signal into one luminance and two color signals. VGA is basically the same as component but with a different connector. VGA and component are the best of the analog video connections. DVI and HDMI are both digital and are the best video connectors.

Of course, like I said above, you can't really improve on the source. If a VCR had a DVI output the quality could actually be worse due to the analog to digital conversion. Stepping the composite signal from a VHS tape up to an S-video or component signal wouldn't yield a better picture.