I'm using mamewah--looks great at 640x480 and I'm told, although didn't work for me, that it also looks good at a non-interlaced 640x288 (less flicker)
mame32 would probably look slightly crappy on an arcade monitor because it's detail level is higer than most arcade monitor's will display--all those little icons which look sexy on your pc just look like colored blobs on an arcade monitor.