Whew... that's a gpood question. I haven't traveled to many islands, actually. Before I had kids my travels were mainly to the more famous places in the 4 main islands, and since then I haven't traveled much at all. I really enjoyed Miyajima island. I had a friend who visited Hashima island and thought it was great (you can see photos he took and read his thoughts here: http://gakuran.com/gunkanjima-ruins-of-a-forbidden-island/)