Svideo:
Seperates the video stream down to 2 channels. The Luminance channel (Black and White) and the Chrominance channel (Color). The are then decoded to RGB at the display device. Sometimes the Luminance is also referred to as the Y channel and the Chrominance is referred to as the C channel.
Component:
Seperates the video stream down to 3 channels.
A Luminance channel (da Black and White), a R-Y channel (Red minus luminance) and a B-Y channel (Blue minus luminance). Then these signals are decoded and the Green is calculated. Because RGB are the three primary colors we can take the luminance channel along with red, and blue, and then calculate what green is.
Basically what Component gives you is more bandwidth (resolution) and is ideally suited towards high resolution sources like Progressive DVD, and HDTV signals.
Bottom line is this: Under every situation Component will give you superior picture quality in comparison to Svideo.