I have similar thoughts on the Marriott Waikoloa vs. the Mauna Kea. The Marriott Waikoloa is more convenient and not as isolated. There are nice views from the hotel, though the beach is not quite as convenient IIRC. The Mauna Kea's location is wonderful if you want to relax and not go anywhere else. And you can get to restaurants and shopping from there. It's just a minimum 15-20 minute drive generally.

On the Big Island, I personally prefer the Mauna Kea. The beach is so beautiful. But, I go to the Big Island to get away. If you want closer shopping and dining options, the Waikoloa may be a better fit.

For Maui, I prefer the Wailea Marriott. You can walk to the Shops at Wailea, which is really convenient. I've not stayed at the Ritz, but the weather and climate when I've driven up there has definitely tended to be more cloudy than in Wailea.