1) Nvidia 128 GeForce FX 5200 AGP
2) ATI Radeon 120 PCI-Express X300
I have the GeForce FX 5200 - but have the opportunity to trade even for the Radeon X300... what would YOU do?
[Edit for typos *sigh*]
While the specifications on the Compaq Presario models we purchased stated 'available expansion slots: 2 PCI, 1 AGP,' it turns out they are now PCI Express instead.
So it's worth double-checking the bus configuration, whichever way you are going.