Efficiency of NVENC is far greater than Intel Quick Sync/software based x264 encodes, but at the cost of quality. If you rate image sharpness and good quality picture then don't use NVENC to encode video. If you rather speed then by all means use it.
The best compromise is to find software that uses hardware acceleration to speed up encoding whilst using CPU/software based rendering, to help speed the process up. If video editing/encoding is your thing, the CPU is by far the most important, as is total RAM which will aid editing and real time responsiveness of software like Premiere Pro considerably.
Laptops cards tends to be far more expensive and inefficient than any desktop version.
If its for a mobile workstation it would be fine to purchase a 960 or 970m
Now if we are going for desktop wich in my opinion is a far more rasonable option... i would purchase a titan x if im pro rendering videos... the budget choise could be a 1060 or 1070