I voted for Hawaii before I read the thread, since I've been there a few times and I loved it. But since most of you have been there a few times, I don't know.
I have a brother who has been to Alaska, and he seemed to love it, though I think a lot of that had to do with hunting and/or fishing, and I don't know if those activities are things these particular family members of your do. It would be a trip to be in a place with so much daylight though, depending on when that happens.
I'm from California, and have been here my whole life. I don't find it anything particularly spectacular, but scoob described it in a way to make me be proud of my state. I guess he does have a point, so many different landscapes, plus Disneyland. Also, we have Yosemite National Park, which is lovely.