I just got back yesterday from Curacao. I've also stayed in Akumal Mexico (It's about half way between Playa del Carmen and Tulum). We stayed at the Bahia Principe there and enjoyed it. They were kind of different types of vacations. Mexico is better for things like night life, while Curacao is a perfect place to dive and chill on your private deck and listen to the waves. I'd like to go back to both. I think the diving is better in Curacao.
FWIW we stayed at All West in Curacao and had a great time. Diving is easy, lots of shore dives or you can go with the boat diving if you'd rather. We did a bit of both. I was concerned about theft I had read about. However, we dove at a quite a few beaches where we were the only car. Never had anyone go through our stuff. No break ins in our room. All in all a pretty darn good trip. I really have no complaints other than that it was a bit too short.
If you can it would be easier to fly directly to Curacao. We had tickets that we needed to use with Continental so we flew into Aruba and flew over to Curacao with Tiara Air because the flight to Aruba was about $200 cheaper. The flight over was easy enough, it's only 35 minutes or so and there are quite a few trips per day, but I didn't factor in the extra cost of airport taxes. You'll end up paying $32 each way, so it ends up adding $64 in taxes plus another $110 for the flight and it ends up as pretty much a wash, and it more hassles to make an extra connection. Also Tiara Air only allows 17kg checked and 6kg carry on.