Im giving my older computer to my little cousin but was wondering if should i put in another video card in it?

The computer has an onboard video card nvidia 6150 i think but i also have a nvidia 7300 gt, and a ati 9250 laying around. Which one would be better to put in? The 7300 gt has 256mb memory, and the 9250 has 128mb i think?

The computer is running vista, but that shouldnt be a difference since both mentioned cards are much better then the onbaord one