EAFF pretty much hit it all. One thing to consider about the NK 321 override pay, however, is that it’s based on a percentage of 321 vs. 320/319 block hours. NK has more aircraft on order and deliveries currently coming, but they are exclusively 319 and 320s. So, as new aircraft come online, the 319/320 block hours will become further disproportionate to 321 block hours thus reducing the override pay. While the 321 override is nice and something I do wish we had, it’s a moving and variable metric. So, I wouldn’t weigh that too heavily in your position.
Congrats on having offers from both! I’m sure you’ll make the best decision for your situation. Always remember that living in or near base is key to money and happiness in this business. Commuting is expensive. Which airline has a (junior-ish) base closest to you?