I think the decision should be based on what you want to do on Oahu. Aulani is on one of the more isolated areas of the island and is more arid. Frankly, there are much more beautiful/tropical parts of Oahu. However, the resort is gorgeous and the service is what you would expect from Disney (I have visited the resort but not actually stayed there overnight). The pool facilities are great, as are the beaches with the lagoons (for swimming, but not snorkeling). You also pay Disney theme park prices for all the food on the resort - $20 for a hamburger type of thing. If you want to lounge around the beach and resort mostly, it might be worth the money. But, if you want to spend most of your time exploring the island, culture, local food, etc., I would not spend the money. It is one of those resorts I will stay at one day when I just want to relax for a week.
Hale Koa looks nice, but realize you will be in a fairly large city. When you leave the resort, you will be surrounded by skyscrapers and traffic. We generally avoid that area of the island. But Diamond Head is famous, as is Waikiki Beach there. Some people really like it.
If it were me, I would consider the North Shore. The waves calm down by May. It is very tropical. Great local food. Polynesian Cultural Center. It is somewhat secluded, and you would need to drive far to see things like Pearl Harbor or Honolulu. But it is my favorite part of the island. We have also done VRBO near Lanikai Beach and it was great. Probably one of the prettiest beaches on the island, smallish town, and not too far of a drive to the North Shore, Honolulu, or great snorkeling. You are kind of between the two big tourist areas of the island.