In Aruba we loved the Butterfly Garden. The rest of the island was ho hum ... the "Natural Bridge" is not much.
In Curacao, I strongly recommend making arrangements for the Sea Lion Encounter at the Seaquarium! It was a kick. If you like you can also do the Swim With The Sea Lions.
We felt perfectly safe in both ports. Of course we stuck to the main tourist areas with our guide.
Check out our trip report and pictures at The Halls Southern Caribbean Cruise
Have a GREAT cruise!