any part of the Caribbean is going to be warm in February. It all depends upon what you are looking for and want to do.
Some general guidelines: Eastern - breath takinginly beautiful beaches with good snorkeling and good shopping. Western - more adventuresome itineary - Swimming with the Sting Rays, Dolphin Swims, Waterfall climb, river rafting & tubing, Mayan Ruins, amazing snorkeling, good beach fun. Southern- most diverse culturally and the most port intenstive itinearies. Which appeals to you the most?