An arcade monitor will always look better than a TV.
Is that an absolute, even when talking about multi-purpose cabs running things like PC games and console emulators? I would also be wanting to hook up a PS2 and/or Xbox to it seldomly...
Well, if you want to hook up consoles to it, that might be reason enough to use a TV. Otherwise you will have to get some type of converter to feed an NTSC signal (s-video for example) into an RGB arcade monitor as well as a switch of some sort to select the various inputs. As for console
emulation, they all look fantastic to me on an arcade monitor (they also looked very good on a TV though).
Here's my general rule of thumb opinion...if you already have a good spare TV sitting around, use that to get started (you can always go for an arcade monitor later). If you are going to have to buy a display either way, spend a little extra and get an arcade monitor. Just my 2 cents.