We have been to Aruba a few times (once for a week) and we spent part of a day at Palm Island where they offer various water sports and such. A neat thing to see is the hotel near the pier where boats travel under the street to the hotel and navigate their way in and out with guests.
We have been to Curacao on our last cruise and found this Dutch Island to be much prettier that its counterpart Aruba. The Queen Emma Bridge is neat to travel over and the swing bridge in the downtown area a must to see in operation. The buildings are so beautiful as the ship comes into the port; so many great colors unlike Aruba stark appearance. We enjoyed this island and did a snorkel to a sunken ship...This tour (I think through the ship) allowed us to get a great feel for part of the island as we traveled to our desitnation to pick up the snorkel boat.
Hope this helps.