If you like hiking, try this outfit on St. Lucia....we did the advanced Rainforest Hike. It was a long day and included a tour of the island - had a great time.
On Barbados we did the catamaran cruise on Silver Moon because they offer a much less crowded boat if you want to pay a little more, but I hear good things about all of the cat cruises.
Antigua was difficult for us to find something active, but we settled on this outfit. It wasn't spectacular but we had a good time. Nice beaches are everywhere.