You don't mention in your post whether you have been to either Cozumel or Curacao before. (Your post could be read as implying you have been to neither, but it's only clear you have not been to both.) They are very different from each other. Cozumel is, of course, a classic Mexican tourist town, with all the margarita bars, restaurants, cruise shippers, and shopping experiences that come with that. Curacao is a big, diverse island, and I was surprised at how urbanized some of it is, though if you want to get away from it all, you can. It's spread out. What kind of topside activities are of interest to you? Curacao's capital, Willemstad, has a great historic center. We enjoyed the Dutch history and architecture. Overall, I think we prefer Cozumel because we just like the whole Mexican vibe--food, language, etc. It all depends on what kinds of things appeal to you.