There's not much difference between them.
The FX gives like 10% more frames per second in games.
And the Radeon doesn't have a full DX9 hardware support unlike the FX.
So i'd pick the FX.
Skyline_man:
Well i have a lot older card than you do: Ti4200

.
But again i'd suggest you buy the GeForce 6600GT.
It's the best bang for buck.
You can get one for like 150€.