I was there last September. I stayed at the Royal Kona Resort. Don't think I'd stay there again. Waikoloa is aweome if you can afford it.
All things being equal though, I'd skip the big island and go to Maui. My experience in Kona was bad. The locals seemed to go out of their way to be a-holes. They would drive up and down the streets in front of the restaraunts and lay on their horns all the way up and down the strip. If they wren't leaning on their horns they would blast their music. Just plain rude. I'm never going back.
Maui works for me. Headed back for the 10th time this September. Lahaina, Kaanapali, Keihi... I've stayed at all three and have always had a good experience. Lahaina is my favorite though.