Haven't been to Jamaica, so all I know is what I hear. Almost everyone says "Don't leave your resort compound", which sounds like some sort of punishment to me. I have met a couple of people that have explored the island on their own, but it seems like they were pretty savvy/adventuresome/not-worth-robbing types.
But I have spent a lot of time on some of the other islands.
I am more of a stay in a small inn, hike/drive around and explore kind of guy than a stay in an all-inclusive resort person, so FWIW:
My favorite is Puerto Rico. The people are really great. Get out of San Juan (although hitting the little bars in Old San Juan is really cool) and see the countryside a bit. Steer really clear of La Perla in Old SJ- got shot at once there. Get away from the bad inner-city element, and Puerto Ricans are the nicest people I've met anywhere. There are some bad apples here and there, but they're usually easy to spot. Vieques and Culebra are really cool; Vieques has a little bit of a rough druggy element in town, and a lot of ex-pat substance abusers bumming around, Culebra is pretty mellow.
St. Thomas is nice, but Charlotte Amalie has a rough Rasta element and some crime. Got a knife pulled on me there years ago. Get out around the island, though, and there are great beaches and it's very beautiful.
St. John is like la-la land. Relatively quiet, safe, extremely beautiful. Great beaches. More high-end, boutiquey.
Tortola has beautiful scenery and that cool yachting vibe. I was there during a garbage strike and a holiday, so my experience wasn't the greatest, but I'd try it again.
Jost Van Dyke is wacky and has a great beach. The opposite of a resort, very small and quiet.
Let's see... St. Martin I thought sucked, at least the Dutch side. Gross tacky tourist trap. On the French side got robbed of all my high-end camera equipment, and got the impression from the police that it's basically to be expected. The French side does have some great French restaurants, especially in Grande Casse (sp?). The beaches and general scenery are mediocre, IMO.
Saba is flipped out, and incredibly cool. No beaches- I swam off the harbor jetty. Clean, safe, tidy, German/Dutch work ethic. A diver's paradise. No big hotels, but nice little inns.
St. Kitts is different, and pretty cool. The beaches are mediocre. Driving around the island is interesting, and the whole sugar plantation feeling is interesting. Some really nice inns and restaurants. Not super scenic. The locals seem pretty cool for the most part.
Dominica is really cool for the first few days, but can wear you down a little bit after a while. Very scenic, great mountain drives, hiking. Very hot and humid and jungle-ey. A lot of critters- I had to swerve to avoid running over big road-kill boa constrictor. The locals are pretty cool, but a little funny at times. Overall, Dominica is pretty spartan, with few creature comforts, mediocre restaurants and beaches.
So that's where I've been in the Caribbean. If you're looking for resort/golfing/shopping/night life, I can't help you (except that San Juan has cool night life.)
Oh- and summer in the Caribbean is BRUTALLY hot and humid, and I avoid it if I can.
If I can provide any more specific information about any of the places I've mentioned, let me know. Good luck.
David