They're close, but S-video is better than composite because it keeps luminance signal separate from the chroma (color) signal. And component is better than both of them.
From best to worst:
1. HDMI/DVI (digital)
2. Component (analog)
3. S-Video
4. Composite video
5. RF-modulated (analog antenna/cable)
And of course only the first two on the list are capable of HD or even 480p. The other three are 480i interlaced only.