Welcome to BN!
You'll get a lot of different opinions regarding Hawaii
If you look at the thread referenced above you will find opposite opinions on which island is "best." But which island is "best" depends on the person taking the trip. We love the Big Island and have been there three times. The volcano is fascinating, there are beautiful botanical gardens there are tons of historical spots and pictographs. If you want constant sun (but kinda deserty foliage and a moonscape of black lava) the Kohala area of Hawaii can't be beat. If you want rain forests Hilo and the volcano side of Hawaii is spectacular...the black sand beach is unbelievable. We stayed at a couple of wonderful Bed and Breakfasts there. Kalekilohana near south point (remote location not much there, lots of authentic Hawaiian culture) and Honu Kai just up the mountain from Kona (lots going on there and incredible hosts who will help you with everything). Both were incredible experiences.
We have been to Maui. It was very nice. I remember being stuck in traffic a good bit every time we wanted to go to Lahaina...but that was a relatively minor inconvenience. We took some beautiful drives while there.
I have to reserve judgment on Kauai. We were there during very bad weather. The beaches will piled with several feet of debris, the golf courses were under 3 feet of water, you couldn't go hiking nor kayaking for fear of a flash flood. Several people were killed in a flood that closed the only road to the north of the island a couple of days after we left. I'm sure when it isn't raining 24 hours a day that it is a lovely island
We've been to Oahu several times since my husband goes there for business rather frequently. I love Iolani palace and if you get out of Honolulu/Waikiki, there is some absolutely gorgeous scenery. Well the scenery in Waikiki isn't bad, but it can be rather crowded. Lots of great restaurants there.
No matter where you go, you will love Hawaii!