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OK, I am making a list of must dive sites
If anyone has any other favorites and descriptions, please let me know
If you haven't been there before, you'll dive the "must dive" sites by default. You must dive any of the Palancar sites (4), and you will. Palancar Gardens, mentioned above, may well be your first dive of the trip.
All of the first dives, with a few exceptions, will be at a site with huge structure. Mountains. The second dive will be on patch reef, generally speaking. First dives are usually 80' max and the second dives are usually 45' to 65' max. First dives are usually less current and less fishy. Second dives are usually more current and more fishy.
Unless you're there for a few weeks, you won't be able to dive everything, and even for a week, you won't get home having "missed" anything. It's very likely you'll want to go back and see more. If you want to do yourself a favor, keep track of where you were so that on the next trip you have an idea of sites you'd like to dive.
My suggestion would be to go with the flow and if it comes up that you're going to a site you already did, mention that to the DM and they'll likely pick a different site if conditions permit, which they almost always do.
You're going to have a great time.