Hawaii doesn't have fabulous beaches, in my experience, no doubt I have missed some. Hapuna Beach makes the odd "best beaches" lists, but in my view, it is not special, and there is a lot of rockiness offshore that can ding your legs pretty badly. There are interesting beaches, black and green sand, with turtles etc. When we go, we might spend a week there and never go to a beach, or go once. There are other things more of interest to us.
We usually go to the Big Island, which is quite different from the others.