Interesting thread.
We all have opinions and no one is flaming yet, very cool.
I've seen both the Radeon and a Ti 500 side by side.
As far as looking at them, they both had excellent 2d. I couldn't see any difference.
The 3D though was a different matter. The Ti seemed to have a richer color and definition of the scenes textures looked better. BUT that is completely subjective as my opinion may diferent than someone else's.
The deciding factor should really be who is more compatible.
That would go to the Ti 500.
Ati's drivers throughout the last several years have left a lot to be desired in 3d. Granted they are trying hard with the Radeon line, but in my experience the nVidia cards offer more support.