Fortunately Nvidia and ATI both have excellent closed source drivers for Linux. However as a software developer, closed source is not for me or my box. ATI is the only viable option if you want to use open source drivers. Nvidia does not seem to want to support the open source community.
I've seen somewhere that Nvidia claims it's because of patent issues.
If you, in this case, don't care about if the driver is open or closed source. Which one is the superior in Linux? ATI or Nvidia?
Jim
/Anders