I love Oahu...never been to the other islands though....
you have city life, some great eats, japanese tourists!..and if you want it quieter, head down to the north shore....stayed at Turtle Bay resort last year, which was fucking awesome......every room had a kickass ocean view.
me, personally would probably get bored on the other islands....I just LOVE getting hammered at Dukes on their patio, listening to the guitarists string along while enjoying the ocean view. Doesn't get better than that.