I would never use composite video for a MAME cabinet. S-video would be my limit.
If at all possible use component video or RGB.
Superior for web browsing maybe, not for std res games....
I do not agree. Although televisions often have the advantage of having lower dot pitches compared to your average PC monitor I believe that is outweighed by the image quality that you will get using an RGB video connection like a VGA cable provides.
Arcade monitors monitors accept only RGB signals and do not have much of the interference and dot crawl that is common to composite video signals. However, this is minimized when using S-video, or Component (YpBpR) connections.
The best thing about using a pc monitor is that it is often possible to run arcade games in their native resolution by doubling the refresh rate of a given game. Although this gives quite harsh scanlines on some monitors, I believe it is the best way to preserve the original appearance of the game, and also gives you pixel-perfect full screen video.
Now, if the TV has a SCART connector, or you have access to a colorspace converter then things start to be a little different.