If you plan on getting an ActLabs TV light gun, then I would go with Nvidia and not Radeon since some Radeon cards do not interface nicely with the ActLabs TV gun. The display screen is shakey and not centered.....
The card I had trouble with was a Radeon 7000. I called ActLabs and they told me to get a different video card..... so I used a cheap Nvidia card instead and everything worked fine.
PS: The Radeon card works fine for Mame though, just had trouble with the light gun.