Both ships you have listed have mostly American crews on board. While I believe NCL America will eventually find great American crews, passenger reviews to date indicate there are many bad apples on board. But many passengers have also reported some great crew members amongst the bad.
Let's hope you find the few great crew members are serving you and your cabin. As for which ship to cruise on, it's a "toss up" to date. I suggest picking the ship with the best departure date, and the best itinerary for you.
Both ships, for example, do not sail pass the large volcano on the big island. So check the ship's itinerary to help answer your choice.