Sennheiser or Beyerdynamic?

Max budget $600, non-wireless, open back. I own a Benchmark DAC combo-headphone amp. Comfort important, but sound is more important. 

I’ve heard good things about BD’s Amiron home model. Also the Senn’s HD660. Anyone done an A/B shootout or own both?  I’m into hi rez digital and DSD music of all kinds... mostly pop/rock/folk/vocals and natural recordings of acoustic string instruments. Also Jazz and Classical. 
Well, this is what the straight talking headphone enthusiast Ken Rockwell said in May 2018.

"These beyerdynamic Amiron Home are the best-sounding open dynamic headphones I've heard. These Amiron Home sound even better than my previous favorite, the much less expensive professional DT 880. For casual listening the DT 880 sound nearly identical, but if you listen to vocal, choral, symphonic, classical, baroque or other completely acoustic music for hours on end you'll appreciate the better smoothness, openness, depth and detail in these Amiron Home." 

I'd personally also like to hear some Grado woodies, and maybe the Audioquest Nighthawks, but I don't believe you can go wrong with the beyerdynamic's.
Beyers are made better and sound more natural .Also cheaper models 
like the DT 990Pro are still being made after several decades  because they still are doing the job !
Lol @ Ken Rockwell.

If you want to keep some money in your pocket, get the Massdrop Sennheiser HS-6XX. At the high end of your budget, get the Massdrop Focal Elex.
the blon b20 ($450 on massdrop) are open-backed planars, very comfortable and sound great---not a western brand but would be my pick in that range
Thank you all so far for your replies. Really great info so far. So glad to be a part of the AG community!
BD DT 990 PRO’s perfect for longer listening sessions. Very comfortble and a non-fatiguing pro sound. I change to AKG 701Q when I like to have a closer look at a specific sound or instrument. A little sharper but also not as comfortable and fatiguing (for me). DT 1990 may be a fine all-round choise. Don’t forget the Philips Fidelio X2 if you can find one. Mucho appreciated in this price range.