Some resorts, restaurants and tour operators on all of those islands will be closed on all of those islands in September/October but you should still be able to find enough that are open/operating to keep you busy/entertained no matter which island you choose. You just have to realize that at that time of year your choices are going to be somewhat limited.

Now, St. John will have the best snorkeling, great hiking and some very picturesque beaches but its a small island so you'll find the highest percentage of "seasonal closings" on that island.

St. Lucia is the largest island so you'll have the largest selection of "open" resorts/restaurants/activities and the most hiking however you'll find that island has the least snorkeling and much darker sand beaches of the islands on your list.

Antigua has the most beaches (some 365) of the islands on your list, not too much snorkeling and will have some seasonable closures but you should still have plenty of restaurants, beach bars, resorts and excursions to choose from. There's some but not a lot of hiking.

Anguilla has the best beaches of the islands on your list and 80+ restaurants, a number of which will be open although some of the more gourmet places will be closed or operating with reduced schedules. The island has some limited snorkeling and very little in the way of hiking.

I've been to all these islands. Although Anguilla is my favorite, St John is right up there. (I will be going to both next month!)

Based on what you would enjoy, I recommend St John. Captain Joe has an awesome catamaran (brings it over from St Thomas to pick you up), prepares a great lunch, is lots of fun and finds great snorkeling spots. He no longer takes his passengers to Jost Van Dyke which is one of my favorite things about sailing when near St John. Hiking is awesome on St John as well as the many quiet highly photographed beaches.

Now I can't wait to be there again in May!

No, but I've been to Mexico a couple of times and the Bahamas once during that time frame. It's not worth the risk to us anymore, so we don't go during those months anymore.

Can you wait until the first or second week of November or December? The weather is usually better. We've been going during those times for the past several years. We had more weather issues in the US trying to get out and come back in with snow and storms than any issues in the Caribbean with weather.