Well, what's good for one is not necessarily good for the other. The Neo Geo was made to be played on a Low Resolution Monitor, and will look blocky and jagged on a higher res VGA monitor (Even though I have seen a few at medium res and they looked alright). A Dreamcast on the other hand would greatly benefit from the higher resolution VGA monitor... so as you see, it is really going to be a per system thing, unless you can live with the jaggies on the Neo Geo.
-Nick