I've tried Mame32, MameWah, AtomicFE, ArcadeOS and several others.
Of all I've tried, I think ArcadeOS (for DOS) and MameWah are my favorites at this point. ArcadeOS gives you a lot of control over game-specific configuration without having to edit INI files. AtomicFE seems very fancy, but geared towards high-end PCs and probably not a good choice for arcade monitor setups. I had a hard time navigating menus with AtomicFE. It seems to have promise but it isn't very user friendly right now, especially when it comes to managing game lists. MameWah also isn't the most user-friendly system, but it is solid and simple after you get it initially configured. I'm enjoying tweaking MameWah right now, though I'm having some weird issues under Win98 that might not be a problem under XP.