i've been to...
the dominican republic (punta cana area):
- mass tourism
- often huge resorts
- very, very nice beaches though, just what you expect of the carribean
- nightlife often only concentrated on the resorts
- almost no getting in touch with locals as tourists stay in resorts
tobago:
- wonderful island
- quite quiet, little nightlife
- nice beaches as well, but not the endless and pure white ones!
- easy to get in touch with locals, as hotels are smaller and tourists can easily discover a bit of the island or surroundings
grenada:
- wonderful island, even liked that one better than tobago!
- little more nightlife than tobago, but far from a pulsating party metropole
- very nice people, nice places and beaches. again, no endless-pure-white beaches
barbados:
- a bit snobby IMO
- quite a bit of nightlife
- everything seemed extremely expensive to me there!
--> i guess for nightlife, the best carribean islands would be puerto rico and jamaica, but i haven't been...
--> what about playa del carmen or cancun? yes, mass tourism - but there you definitely get nightlife (if that's somewhat important)