The Laserdisc is encoded in composite video, so if the Y/C splitter circuitry in your player is not superb, then you will actually get a better signal via Composite han via S-Video.
If you can get an RGB player, try it - the higher bandwidth on the RGB connector tends to give you less dot crawl and better definition, but once again, only if the players splitting circuitry is up to the task.
*Most* laserdisc players give a better result via composite.