Dual Video Cards ... ATI or NVIDIA?

Looking to replace my internal ATI RADEON XPRESS 200 Series 256mb to get better quality as well as speed at ... at high resolutions

The reason I ask ATI or NVIDIA is because I was a big fan of NVIDIA until my computer came with the internal ATI, I've had no problems with either...  is it just  Pepsi/Coke ?

>> ATI video drivers are fantastic. The catalyst software they have for windows is awesome as well.

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