I have heard that bermuda is lovely...but I don't know about the nightlife. It is definitely peaceful and beautiful. Maybe Belize? I've been there and the beaches are amazing...but I'm not sure about the nightlife (I was 16 the last time I was there!)
when I researched this recently, St. John was the most appealing to me. It looks beautiful and there is a National Park there for hiking and general nature stuff. You can also take a ferry to St. Thomas and check that out too.
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I loved the Virgin Islands! St. John is smaller and more beautiful than St. Thomas (which feels a bit commercialized and plain to me). I was there with my family, so I can't really say on the romantic part, but if you go, do make sure you're somewhere that is air-conditioned. We stayed in an amazing eco-camp/lodge, but it was open air and the islands are very hot and muggy. You don't want other people to come near you when you're feeling that hot and sticky! ::
dominican republic, belize, puerto rico. highly recommend placencia in belize -- we went there on our honeymoon. it is in the south and doesn't have the loads of tourists as the northern part of the country.
St. John is really beautiful -- I was only there once about ten years ago, and it was with my parents and grandparents, so I can't exactly comment on the romance factor. But to be honest, it wasn't my favorite place, although it was a long time ago so take that with a grain of salt. Have you thought about Grand Cayman? They have shopping, nightlife, restaurants, and great snorkeling/diving if you like that.