I liked Aruba, but they neglect to tell you that the gentle year-round "breeze" is sometimes strong enough to knock you on your ass. I found Grand Cayman to be fairly crowded with rotten traffic, but for scuba/snorkeling, it can't be beat in the Caribbean. Jamaica blows. Ditto St. Thomas. (St. John is infinitely better.) In Cancun, go to a resort and don't leave it.
For the record, I wasn't all that impressed by Oahu or Maui either.