I've ben to both, funny enough on the same trip. Liked them both a lot, but for very different reasons. It was my first trip to the Carribean. We spent 5 days on each. In Aruba, we did one guided dive (we were very new divers) on a reef, doing a backroll off a pier. We also snorkeled twice, once on the wreck of the Antilla, the other at De Palm Island. What we saw on the reefs was pretty, and in retrospect, I would love to go back there and do some wreck diving, but my fondest memories of Aruba are from the land, not the sea. Island is very clean, people are all friendly, crime is almost non-existant. Oranjestad is a beautiful little city, if you enjoy gambling, the casinos are large and spacious, almost Vegas-like. Night life is abundant, beaches are probably the best we have seen in the Caribbean.
Our experiences in the water in Aruba tipped it in for my wife to decide she wanted to do AOW in Curacao. Once we splashed in Curacao, we began to realize what Aruba was lacking. The colors were unlike anything I have seen, with the possible exception of what we saw on the Atolls in Belize. The reef seemed to never stop. Vis had to be well over 100 ft, fish and coral everywhere! Still some of my favorite diving anywhere. On land, the island is a bit less inviting. The Jewish settlement building are quite a sight for a tourist, but the rest of Willamstad was less than impressive to me. Some historical forts, and a plantation with slave houses intact was an interesting bit of history. The Seaquarium was interesting to us as new divers, but not sure if I would enjoy it as much now as I did then.
Bottom line...I would recommend both destinations, but which one depends on what you want. Curacao is an excellent dive destination with a little bit of tourism built in, Aruba is a fun little party island with some decent diving.
