Rifleman with response to your choices of Islands to visit, I have not been to Grand Caymen, but out of the other 3 the top 2 are Aruba and St Martin. This is a hard choice as I love both.
Aruba is beautiful and the high rise area is wonderful because you can walk to so many resorts, bars, restaurants, and stores without getting a cab or getting in a car. Aruba is small and it is a desert island, so not green and lush but instead covered with giant cactus like you see in the old western movies. The resort areas are gorgeous, but a lot ofthe Island is desert with no greenery except for cactus. My brother likes Aruba best because he never has to drive anywhere (although a car or cab is needed to go downtown, to the lighthouse, to Baby Beach, the donkey sanctuary, many of the best restaurants, etc). He likes to get a cab to the resort from the airport and never get in a vehicle until he goes back to the airport. If you stay in the high rise section you can easily do that.
St Martin is beautiful EVERYWHERE and my favorite. It is lush, green, and there are mountans and ocean views everywhere you look. St Martin has more different beaches than you can visit in a week. To really enjoy St Martin you need a car. There is too much to see. The Dutch side, the French side, Simpson Bay, the lolos of Grand case, the nude orient beach, Great Bay, Little Bay, Marigot, Phillipsburg,watching planes take off and land at Sunset Beach Bar, etc, etc, etc. A friend of mine went to the Belair Beach Hotel on Little Bay for a week and left one time for a tour of the Island. He ate every other meal at the resort (Gingerbread Cafe which has really good food) or in the room, and he said it was one of his favorite vacations ever. He is going back next fall and he said he might not leave the resort at all. The Belair and Divi are the nly 2 resorts located on the entire Little Bay, so t is never crowded and a very relaxing area to lay on the beach and swim. I love staying on the beach there for a day or two, but by not leaving and exploring the Island he missed too much in my opinion, but to each his own.
You won't go wrong with any of your choices, but the Bahamas are my least favorite. JMHO.