ATI RADEON X600XT 256MB DDR
ATI RADEON X700 256MB DDR

GeForce FX6600 128MB DDR

Please recommend a most compatible and effective graphic card from them.

The GeForce 6600 is probably the fastest card, followed by the Radeon X700 and finally the Radeon X600 XT

It's hard to judge compatibility and suitability, when you've not submitted any machine details or games you wish to play, but I'll give it a shot.

The 6600 is a more advanced core technologically, in the same vein as the 6800-series. The X700 is a intermediate product, to fill the game between the high end X800 and low end X600 series, which is more or less the 9600 core in PCI-Express form. Since X700's release, the X800 series has filled out to include over 10 different models, completely occluding the X700 as a viable card. The X700 Pro and impossible to find X700 XT have a bit more go, but are obsolete cards.

The X700 will win the odd benchmark, but it does so with inadequate consistency.