Guadelupe is one of the most beautiful islands I have been to in the carribean, but it is rather expensive. There is a lot to do if you like snorkeling and hiking and nature activities.
If beaches were an issue, I would suggest St. John’s (but the good places are pretty expesive), Antigua or the Bahamas. I really liked Antigua, but if you are not going for the beaches, then I think Dominica or St. Lucia would be a far better choice. I have not been to St. Lucia personally, but the friends and relatives that I know who have been there have all said it was a terrific place to go.
Barbados is big, and has a little bit of everything. The prices range from not bad to really expensive depending on where you want to stay. I don’t think the island is as pretty as many of the others. I was not too crazy about the beaches there. There are some good places to see, but you won’t find any rain forests to speak of like you will in Guadelupe, Dominica or St. Lucia.
Jamaica is not a bad place either. There are places to go and hang out, and there are plenty of day trips to the falls or shopping and such.
Dominica is indeed beautiful, and when we were there about eight years ago, the people were really friendly. There is some great snorkeling and diving (I think the place we snorkeled was called champagne reef. If you ask the locals for the best place to go, they will tell you. There are two main snorkeling reefs, as I recall, but champagne reef was the best.) Dominica is quite small, but it should have enough to keep you occupied for a week.
Just so you have a basis of comparison, I was not overly impressed with Grand Cayman, but thought Aruba was beautiful. (I thought the Cayman beaches were way overrated, but that is just me. The diving was incredible though).
It is hard to say where you should go, because I am not you. If I had to list the islands in order of my personal preference, they would be:
St. John’s - Beach $$$
Antigua - Beach
Bahamas - Beach
Guadelupe - Nature $$$
Dominica - Nature
Jamaica - Beach and Nature
Aruba - Beach
Barbados - Rum
Grand Cayman - Diving $$$
If you are into ecotourism, then you would probably really like Costa Rica. The rain forests there are amazing. I really love Cancun. There is a whole lot to do there, or you can do nothing. They have good beaches, fishing, the mayan ruins, etc.
Just so you don’t get the wrong idea, I don’t spend every summer in the carribean. Several of those islands I have only seen because we were on a cruise. While you can get a good feel for the island in a day, it is not the same staying there for a week.
Good luck, and Bon Voyage!