AMD does seem to have a renewed focus on its Linux drivers, thanks to Valve's Steam Machine push. But AMD graphics certainly won't be competitive with Nvidia graphics when the first Steam Machines launch in November.
If a manufacturer releases a Steam Machine with AMD graphics that seems like a good deal, it probably won't be. Even if it has a newer or more powerful graphics card than similar Nvidia-equipped machines in the same price range, the Nvidia-equipped machines may very well perform better--though that can and may change over time, of course.
What about Intel graphics?
As we debate AMD vs. Nvidia, it's worth nothing that Intel's integrated graphics aren't really in the running. Intel does have solid open-source drivers, but its integrated graphics would work only if you plan to use a Steam Machine to stream games from an existing Windows gaming PC or play a handful of less-demanding games. But you'd be better served by a $50 Steam Link to stream games to your TV. For actual Linux gaming, choose Nvidia.
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