Transcoder here, if you're looking to leverage quality/file size benefits of your codec, you don't encode with hardware.

As a rule of fist hardware encoding is better served for streaming purposes where you need to crush a raw 1080p or 1440p stream into something that's actually a sensible bandwith as fast as possible, especially if you're streaming 60fps because your algorithm has a time limit of 16ms per frame.

If file size with preservation of quality is something you care about, you encode as slowly and thouroughly as you can, which is why x264 on your CPU will outperform encoders like NVENC any time.

When it comes to HEVC, software encoding is only really worth it if you have the time to spare, because x265 takes between 3x and 5x as long as encoding the same footage through x264, with a 15-20% smaller file size at best. It is also more intensive to decode, which is why you still see many files with a H.264 codec.