Hey Mark,
First you'll need to decide if you want a Dive Vacation (diving first, up to 4-5 dives per day, then other items come after) or a pleasure vacation with some diving included. Do you want other amenities at your resort or just basic with the focus on diving services? Beach? Swimming pool? Disc? Party crowd? Family style? Basic hotel room, basic food, lots of diving?
We've vacationed and dived Jamaica, Bonaire, Bahamas, Cozumel, FL Keys, Playa Del Carmen (MX) and others. The vibe is different for each and the commitment to diving varies with each resort. I'll try to give you my thoughts on these destinations.
Bahamas and the Florida Keys are good diving destinations but they tend to be more expensive, although you can do Key Largo pretty cheap if you stay at the more basic hotels and use the small, local dive shops.
In Jamaica, diving is just another feature of many at the resort, if offered at all. Many resorts are all-inclusive for rooms, booze, activities, and maybe even diving. They usually offer only 1-2 dives per day to a very nice and safe reef. The diving is beautiful, warm, clear and easy, but not very exciting for experienced divers. Dive masters lead every dive and will help you along. Dive times are closely controlled and you may not dive without a local dive guide. The beaches are generally excellent, the services good, food can be outstanding, and there are plenty of activities on and off the resort. If the resort doesn't offer diving then dive services can be hard to find. Jamaica moves slowly so you'll need to get used to "soon come, mon" while there. (Oh, and you will be offered drugs frequently when on Jamaica, some people love this but I get tired of the constant offers.)
Bonaire is a long, usually expensive flight. The island is south of the hurricane belt so it avoids most bad weather during hurricane season. The island is very dry and there's not much to do when not diving. Many people book a hotel and a small rental pickup then rent tank (sometimes all in a package) then go diving by themselves from many, many marked reefs around the island. You can also stay at resorts that have both shore diving and guided boat dives available. There are only a couple of resorts with nice sand beaches, most have rocky shorelines or rough rock beaches. All-inclusive is unusual here. This is a great place if you want to be on your own to discover the island and dive on your own schedule without others in a group. The water is clear, calm, and the reefs beautiful with lots of fishes.
Mexico has a mix of all-inclusive super-large resorts all the way to little private hotels. On Cozumel, most hotels have diving services on site with several options for dive-included packages. Some are small hotels that will include breakfast and many dives with the on-site operator, or you can choose your own dive op if you want. There are large all-inclusives that have many features, great beaches, lots of activities, and an on-site dive operation. These are available on Cozumel, Cancun, Playa del carmen, and many other areas.
For a totally dive-centric Mexican vacation I would suggest Scuba Club Cozumel as a great place to stay and dive. Nice small resort within walking distance to town, great dive services, nice food if you want it included (optional). They have shore diving and many boats that go out several times per day. They will put you in small groups based on ability and experience. If you need assistance, they'll be happy to help. No real beaches on Coz and the pool at the resort is tiny. The point at SCC is to dive then relax.
For all-inclusive vacation with diving, I really like Iberostar Resorts in both Cozumel and Playa Del Carmen. Great hotels, great pools and beaches, good dining, plenty of activities, and really good dive services with the operator Dressel Divers. Not as many dives per day but they do have dive guides with every group, full instruction, nice boats. The Cozumel resort is only a 5 minute boat ride from the best diving in the world. Easy diving, beautiful formations, bigger fishes, but some days can be challenging if the currents are strong. For a really impressive resort with fabulous features look at Iberostar Paraiso Lindo and its' sister resorts near Playa del Carmen. Huge 5-resort complex with amazing features. The diving near hear is really nice, calm, clear and lots of fish life.
For a family or couples vacation with some diving, IPL is fantastic. For an all-diving vacation, I'd go back to Scuba Club Cozumel anytime. It seems that Mexico is also some of the cheapest options in the Caribbean at the moment.
Choose your preferences and have fun getting wet!!
