Nighthawk I am sorry to say is really, for me anyway, not a good choice. Extremely rolled off higher frequencies. At first I found it really interesting, certainly not fatiguing, but it doesn't take long before your brain is screaming out to have the missing high frequency information that it knows is there. I owned the Nighthawk and Nightowl, same story, easy to fall for initially, but just too darn restrained in the highs to stay with. IMO.
Each to their own as they say, I also know some people love those Audioquest headphones. Ultimately let your own ears be the judge. I agree about the DT800. I also owned the 600ohm Premium model. Really liked it, but it absolutely is not easy to drive so if you tend to like louder playback volumes, be prepared to get a decent amp.