My only real experience is the Big Island.

I have a cousin who has a family in Kailua-Kona (he moved there in the 1960's and married into one of the oldest families there).
I also have friends from college who live there, some on the Hilo side and some on the Kona side of the island. I rented a car and drove completely around the island, but stayed mostly on the Kona side. I love the waterfalls, the botanical gardens. I was there in what would be a winter snowbird month, but I didn't notice any overpowering number of tourists on my stay.