First, you should know that although there are several HGVC's listed in Hawaii, they are all on two islands: Oahu or Big Island. In fact, they're primarily in just two locations -- at Hilton Hawaiian Village (HHV) on Oahu, and at Waikoloa on the Big Island.
HHV: Lagoon Tower, Kalia Suites, Grand Waikikian
Waikoloa: Bay Club, Kohala Suites, KingsLand
They've recently added another Oahu location, Hokulani in Waikiki, about a mile away from HHV.
So to answer your question, you need to decide if you'd rather go to Oahu or the Big Island. Oahu/Waikiki is an urban environment - think big city with a tropical beach. Many people love it for all the urban energy it brings, and all that's available. Personally, I don't particularly like it because it's too crowded.
Big Island is a more tropical island feel, albeit a volcanic island. That is, the volcanic rock can be rather stark; but huge resort areas have been carved out, with imported palm trees etc. I think that Big Island has better beaches; and you can go to the other side of the island to see rain forest and the volcano.
Once you decide on an island (no easy task!), then you can decide on which resort on that island. That's a bit easier task; it's mostly a matter of amenities versus number of points. I'm sure everyone here will be willing to throw in their opinions. Even me
-Bob