Neither airline is a good choice anymore. If you move to Atlas you will most likely never upgrade at your age. Kalitta is the obvious choice for you now given your age and longevity. If you were age 45 or less a move to a US Major would be a good idea. If you have PIC on the 400 then look at ExPat jobs like Korean, Saudia, Qatar or Etihad. If you are an FO I would just gut it out at Kalitta until they close the doors.