I always go with NVIDIA. It is the best graphics card for gaming.
In my opinion, NVIDIA is the best graphics.
Video editing actually does not task video card heavily, as long as it's not *D work as already mentioned above. Any modern low-mid range gaming card will work fine for video editing. I tend to lean towards nvidia for Photoshop work. Video editing work is highly dependent on your processor- you want a fast quad at least, 8gig of memory, or even maybe *6 since its not expensive anymore.
A fast hard drive is also a big plus. An SSD will amaze you if you can budget it in.