Depends on which card is the best for me at the time I want it.
I have a Mobility Radeon X1600 in my laptop which is perfectly fine, although it runs a little hot.
I have an Nvidia 8800GT in my main machine which I've been very pleased with.
I have an Nvidia 9500GT in my server for Folding @ Home which I'm also pleased with.
The family machine has SiS integrated graphics which they're fine with.
I've used graphics cards and chips from other vendors, such as Intel and S3 Graphics, and they've all been perfectly fine.
To me it's not the vendor or OEM that matters, it's what's best for me or the user and the machine's intended purpose. I don't think anybody can say "X company is always better" because that's the nature of the industry.