I've been to Kauai, it IS
absolutely gorgeous! Now this was back in '85-'86! Absolutely awesome scenery. Na Pali coast is stunning. (we did it from the air in a helicopter!) The hotel we stayed at had a deal where you could take a brief scuba lesson in the hotel pool, and then the Dive Master could take a group of 5-10 out for a supervised dive! (limited to like 20-30 ft deep, but an actual scuba dive!) I had snorkeled a lot when I was in the service on rotation in Okinawa, but diving was Waaaay cooler!
They also have what they call "The Grand Canyon" of the pacific! I don't recall the actual name, but the drive up the road is amazing. It really is like a lush, lots of green, tropical Grand Canyon!! Bright red rock & verdant foliage. Really beautiful!
If you are considering Hawaii? Kauai is definitely way cool!