Will an AMD Radeon HD 6870 perform well for Premiere CS6? Will I be better off with an NVIDIA card?
I assume you're asking about this on a Windows platform? If so, the AMD card won't work at all with CS6. Adobe hasn't moved their OpenCL MPE code to Windows as of CS6. For that you'll need CC when it's released in June.
Stick with nVidia.
Jason's information is somewhat inaccurate.
Most any graphics card will work fine with Adobe software. Premiere Pro has the ability to use some graphics cards to accelerate certain operations like effects, scaling, frame rate mismatches and a couple others. If you want that acceleration, your best option at the moment is an nVidia card. But even with an ATI/AMD card, the software will work just fine.
[moved to hardware forum]