First, congrats on your job offer at NWA. At least you have "one in the bag"
which is more than most can say. I would go the interview at Delta, but take the first class date you can at NWA. Having worked for both Steenland and Anderson, Anderson is by far the better CEO, I think he actually cares about Delta's brand image instead of just raping the company. NWA's product is crap, they seem to be floating along waiting for the next merger partner, with no thought about its employees. Delta has better duty rigs, NWA lost theirs with the last contract and I don't see them getting them back any time soon. forget the 1.5x over 80, the duty rigs are where it's at.
Delta first, NWA second. I've been gone for a year so I may be wrong, It's a crap shoot anyway.
Good luck