Well I'm no doubt in the minority here in that I do not particularly like the HHV in HNL, Oahu all that much, since it's way too large and impersonal etc. If you go to the HHV I strongly suggest you stay in the Ali'i Tower, a kind if separate hotel within the hotel. It used to be an Amex Plat FHR but I believe that it no longer is.
On the "main" island, as you call it, Hawaii or the "Big" Island as it's often called, I think the HWV (former Hyatt) is much, much better. Though an oceanfront/view room here on the Executive Floor does not come cheaply, the food and service here are excellent. Though I prefer Mauna Lani Bay Hotel or even the Orchid at Mauna Lani (former Ritz Carlton, now a Starwood property), my family absolutely loves and adores this place and would never think of staying anywhere else. Last year I though of trying the new Four Seasons at Haulalai (near the Kona airport) but they woul not even think of it. The HWV is one of Hiltons best Resort properties, IMHO.