I personally would rule out the Marco Island property, even though I understand it is one of the top moneymakers in the Marriott family. The hotel is always packed to the gills with conventioneers and party people and is not conducive to relaxation. The city of Marco has little to offer in the way of sightseeing or attractions although the beaches are lovely. It's a 17-20 mile drive to Naples which is a beautiful city but a bit of a drive. Also, the Marco property always commands top dollar in tariff and in amenities. Although it's not one of your listed choices, I'd go for the Marriott on Hutchinson Island about 50 miles north of FLL. I think you'll have an enjoyable stay whichever Marriott you choose. Have fun!