Nighthawk wins on comfort against any other headphone. I also agree that NH offers the smoothest and easiest listen out there, but it is technically nowhere near to the 2C. NH is smooth, dark, warm, with a significant mid-bass hump. It can also sound a little bit hollow at times, like it was in a cave. Trebles is held back quite a bit, percussion can sound like there was a 'sliencer' on them. That said it is the lushest and easiest listen out there. I loved it a couple of years ago, I still like it but don't consider it to be on the same level as the 2C.Nighthawk wins on comfort hands down. 2C might as well be a torture vice by comparison. Hawks are by far the better headphone for forgetting about everything but the music. You never really forget the 2C’s presence.
The 2C in comparison has a precise and well balanced bass that extends deeper and doesn't have mid-bass hump. It sounds more spacious and more natural. Soundstage is bigger and instruments can breath. Treble is still laid back but has some energy. 2C is also more resolving in comparison.
Both are good headphones for different purposes. I can imagine a scenario when someone prefers to put the NH on his head, but from a technical point of view the 2C is vastly superior. Of course, you need a more serious DAC/amp combo to drive the Audeze to its full potential but if you do, IMO there is no contest between these two.