i'd take a 19" CRT vga monitor over a 19" TV with composite video any day. i'm not an arcade purist though...i dont mind if the picture doesn't look exactly like it did on the real cabinet, as long as it doesnt look like crap.
Composite is crap; component is not. Component is on a similar quality level to RGB, if you can get it to work that is.
i have a 19" CRT pc monitor in my DK mame cabinet and it looks great.
I think classic arcade games look like crap on PC monitors, but it is a different kind of crap than say, a TV through composite, but not better crap. The problem with PC CRT monitors is not due to the lack of a high quality signal, because they use RGB which is as good as it gets. The problem comes from the display being optimized for high resolutions and reading tiny text; it makes those old crude graphics look like Lego blocks.
Also, they are not typically capable of 15 KHz, so the only way to get the low resolution classic arcade games to fill the screen is through either unfiltered pixel duplication (which enhances the Lego effect) or through pasty filtered stretching; neither of which look particularly good.