I would agree that the Big Island (locals told me they preferred "Island of Hawai'i") is a great place to visit. I took all 3 of those day trips in July, and two of them the last time I was there in 2004 (with active lava flows back then). There are marvelous natural sights and of course the only active volcano around.
But I'd still take Maui as my first choice and Kauai as about a tie for second (Oahu is a one-timer - had to see Pearl, Arizona, Big Mo, hike Diamond Head, snorkel Hanauma - but no need to go back now). ALl three island islands have similar scenic drives (Hana and all the way around, all the way around the north/west, up to Haleakala and the high country, both directions around Kauai). But Maui also has activities, kids things to do (if you have kids), water sports, and other items to round out the week. If you're purely looking for natural beauty - waterfalls, hiking, etc., etc. - all are about on par. I just think Maui has the more "normal" things to do to compliment.
I'm fortunate enough to be able to go every two years. After checking off Oahu, I've been pairing Maui with Kauai and the Big Island alternately. It's a tought choice, and one based on personal preferences and objectives, but that's where I ended up. (btw, I can't fathom Maui being a "couple of days" island - we did 10 this summer and still had a to-do list)