For DarkBASIC Professional GeForce cards are much better suited, mainly because basically the entire team uses them, so any bugs that appear on ATI aren't caught until public betas; sometimes not even then.
As for everything else, it depends on which generation.
OpenGL is NVIDIA country, always has been, and despite the XSeries claiming to be the only OpenGL 2.0 cards; it always will be. That said, only a handful of games each year for the PC user OpenGL so it makes little odds in the big picture.
Big Picture wise is DirectX, Shader Support & Speed.
This is where things get a little tricky, this is basically the speed chart for adverage games; remember there will be exceptions to this as cards are 'optimised' for more popular games and programs.
Lower on the chart, and Left of Equivilant is faster:
GeForceFX 5200 - Radeon 9200
Radeon 9550 - GeForce 5300
Radeon 9600 - GeForce 5600
GeForce 4Ti - Radeon 8500
GeForce 5700 - Radeon 9700
Radeon 9800 - GeForce 59x0
GeForce 6200 - Radeon X300
GeForce 6600 - Radeon X600 / X700
GeForce 6800 - Radeon X800
Equivilant in end names are:
GeForceFX - Radeon 9Series
LE - SE
.. - ..
Ultra - XT
GeForce 6Series - Radeon XSeries
.. - ..
GT - PRO
Ultra - XT
Extreme - Platinum
Run down on Shader & DirectX Support
GeForceTi - DirectX8.1 .. Max Shader VS1.1, PS1.3 (PS1.4 - 4800)
Radeon 8500 - DirectX8.1 .. Max Shader VS1.1 PS1.4
Radeon 9Series - DirectX9.0 .. Max Shader VS2.0, PS2.0
GeForceFX - DirectX9.0 .. Max Shader VS2.0, PS2.a
Radeon XSeries - DirectX9.0b .. Max Shader VS2.0, PS2.b
GeForce 6Series - DirectX9.0c .. Max Shder VS3.0, PS3.0
Also remember to note, that Doom3 is an NVIDIA Game and Half-Life2 is a Radeon game; from the benchmarks run it has been determined that..
Under Doom3 each GeForce was capable of outperforming the equivilant Radeon by 10fps, in some cases 25fps.
Under Half-Life2 each Radeon was capable of outperforming the equivilant Geforce by 5fps, in the current card generation (6Series) the max gap was 8fps, in the previous generation (FX Series) the max gap was 20fps.
You can take from this what you will, but considering the GeForce's driver stability history in the widest range of games; plus NVIDIAs ability to seriously optimise the performance of thier cards, leading to the entire FX-Series gaining a 20-44% speed boost over the last year.. it would say to me that combined with thier ability for next generation technology makes them the more sound choice.
Personally speaking, my GeForce have been able to run more games without problem out-of-the-box than any of my Radeons. I feel that is a little more important than 5fps more when you card is already pushing 60+ FPS.
