Try them both with your TV set, and your computer. Sometimes it's better, sometimes its worse.
Often the s-video port is stuck on the back, and just wired together inside with a cap (your basic s-video to composite adapter at radio shack) - in essense, its just a composite video input with an s-video connector for convenience.
Likewise, sometimes component video inputs, if the TV doesnt support progressive scan or high def, are basically the same deal. The jacks are there for convenience, with a cheap analog component to composite adapter inside. In fact, if your TV doesn't support progressive scan, and therefore only component video at 480i (regular old video), you probably wont see a difference between s-video and component.
In fact, on my Phillps 27" set, s-video looks better to me than component, I was pretty dissapointed to blow 20 bucks on component video for my PS2 only to find out it looked somewhat washed out.
Though in the end, to me at least, it's like the frame rate wanking on PC game forums. If you can notice the difference between 50 fps and 53 fps, or see little jaggies in the distance, then either the game you're playing sucks or you aren't much of a gamer. My point is, you'll be looking at the game you're playing, not the screen.
(quick history - composite ntsc was the format that laserdiscs stored, which is when they started appearing. S-Video was the format that SVHS tapes stored, which is when they appeared. DVDs store video in component video, so now they're standard. The good-better-best thing people spout is not a hard and fast rule, like I said above, if the TV has cheaper components and S/Video or Component was added for convenience, don't be surprised if it doesn't look as good as you expect, or even worse.)