It all depends about what you're dreaming about, your willingness to explore beyond a resort compound, your facility for foreign language, your appetite for exotic food, and your budget.
We don't like big resorts and do like to explore on our own. We enjoyed a visit based on the French side of St. Martins, one of the more tourist developed islands. We've also visited St. Kitts several times and find it more "laid back" but enjoyable. We tend to go off-season for better rates, which generally means November. We generally rent a car for at least a weekend so we can be more free to nose about all over the island. We also enjoy snorkling amidst tropical fish and St, Kitts has a great catamaran cruise/picnic for that but do pick a calm day! We had a rough day when we tried that in St. Martin; the sail and the picnic were great but we should never have tried to snorkel in the waves.
We find the websites extremely helpful in terms of picking a resort to base ourselves in, and they all love to provide discounts for repeat customers.