I strongly suspect that as all the airlines re putting prices up, the holidays will be gradually getting more expensive.
There is also the distinct probability that a number of smaller airline will go under.
On this basis, book sooner rather than later, with the most established airline you can, and ensure the airline/agent you book with is ABTA and ATOL covered, so if they go under, you dont lose out.
Also make sure you have travel insurance covering you continuously from when you book. Trips booked before you buy cover wont be covered if things later go wrong.
On the actual destination front. i went to antigua. It is very pretty, and enjoyable, but it is one of the quieter islands, so if you are after a mad party, its probably not the right island.