I would say my need for a ND filter would be for 75% video, and 25% stills. I don't think you could be able to tell in video which brand of nd filter performs better, but how much of a difference is it in stills?
I could just get one 3 stop B+W like this
or a package of 3 Tiffens at 2,3,& 4 stops
The Tiffen set would be more versatile for video, but would the difference be night & day compared to the B+W when shooting stills?