737 contract is better, better pension and a few more perks, also all the 737 bases have union recognition, which love or hate unions, has made Norwegian a better place to work.
Job security, well 787 pilots have never been laid off, or made to take part time.
737 this happened in 2014 and 2015, but seems to have stopped now.
Career progression is excellent in both operations, plenty of expansion so plenty of chances for promotions base transfers etc...