I have stayed at the Marriott on SMB. We were very pleased with it. I can see the argument saying it has a narrow beach, and isn't as centrally located as the Westin. That being said, we never had a problem getting plenty of seats on the beach. Plus the water is very calm, and they have lots of floating platforms to relax on too. As for the central location, cabs aren't too cheap (nothing is on that island tho), so it may save you a little in that sense....I thought the options for dining were very good. We typically did breakfast and lunch there, and on some nights, found some great places off of the property for dinner (Calypso Grill, Sunshine Grill, etc)....The property is very beautiful. I think it was renovated to a certain extent in '14 or '15. The pool isn't huge, but the ocean is basically as calm and just a few steps farther....We dove with Don Fosters because we went with a large group. I think their boats hold 16 and 24 people. So if you're looking for something a little more personal, they might not be the ones for you. That being said, they did a great job and the guides were fantastic. We hit several sites that I did while on the Cayman Aggressor Liveaboard (Kittiwake, Trinity caves, Round Rock), so you wont be cheated on the sites....I have not stayed at the Westin, but I hope a personal account of one will help the decision. Good luck.