When are you going? We are tentatively planning a trip in March. I would like to know about the diving, too.
My impression of the diving in or around
Varadero was not very good. A lot of coral bleaching and not a lot of life. Incredibly beautiful beaches though.
Diving in the area around
Marea del Portillo is mediocre, fairly average Caribbean diving. Some colourful reefs, some sea life, not a lot of big critters. Beautiful area nestled at the foot of the Sierra Maestra mountains where Castro hid for a couple of years before his Revolution.
Diving in the area of the
Bay of Pigs is also pretty average Caribbean diving. Diving in El Brinco cenote (cavern) was fun. It gets pitch dark very fast though long before the cave entrance, so a word to the wise.
We chose not to dive near
Havana and just explored the sights and sounds, walking around, visiting restaurants and having a marguerita.
Jardines de la Reina was fantastic diving! We were on the Avalon liveaboard Tortuga, and we had an excellent experience. Healthy, colourful reef, abundant sea life, and large critters on every dive. Sharks, sea turtles, sting rays, spotted eagle rays, green or spotted moray eels, grouper, etc. on every dive. That was amazing diving and I haven't seen it equaled in the Caribbean. The closest second in the Caribbean was specifically Lighthouse or Glover's atolls in Belize long before they became popular tourist destinations.
Hope that helps to give you an overview of some of the diving areas. Jardines de la Reina has really increased in price the last few years, but If you can make it, it should be quite a great experience.