Go with 4670 only if using windows otherwise headaches.
NVIDIA was always known for excellent drivers.
Seemless suppport for Hackintosh and Linux.
GT220/240 series are designed for HTPC crowd. Latest PureVideo4 provides great image quality, postprocessing and hardware acceleration for Adobe Flash, DivX, XviD and H.264 MPEG2.
ATI4XXX GeForce 9600/9800 as old 2-3 year technology are great only for gaming at this moment. Plus it feels like sitting next to starting jet, not to mention power bills for two-slotters.