I still really love the AMD/ATI cards for video work; and they also play games really well. What it really comes down to is what level of "editing" you plan on doing here.
See, just cutting up videos, splicing, etc...that's not very graphically heavy. If you're rendering video and do a lot of preview work, then you'll really want CUDA and an application that really uses CUDA and not just lean on the CPU for this chore. It's still very rare to find an application that leans heavily on CUDA for the actual rendering process so CUDA may not be worth it to you if you're not doing a crap load of previewing before the render. The only thing I've personally used that hits CUDA is high dollar Adobe products ($1,800), while my other average editing software (like TMPenc) only hit the GPU during the preview. Even Cinema Craft Encoder ($2,200) doesn't touch CUDA as we're talking about a LOT of horsepower/threads needed vise something that's really something pretty simple and not threaded.
So, Yeah...it depends. I feel ATI is still more accurate in the colors for videos if you manipulate them, their Firestream is more of a co-processor than CUDA cores/Shaders are for video work (and more easily pseudo-threaded), and just happens to be very good with OpenGL work. When working on a video project I really spent some time it, I prefer working with the XFX6870 over the GTX570 or 560Ti. Haven't tried it on the GTX670 yet as I'm not expecting any huge improvements in this area as I feel nVidia are truly gaming/folding cards. They seem to be really good at 2D AutoCAD though, which is odd.