I've stayed at the good Marriott properties in almost all parts of Florida - South Beach, Miami Beach, Clearwater, Key Largo, Marco Island, and Orlando. Without a doubt, if you have a family and like the beach then Marco Island is the best. I just got back from the Keys and checked out Key Largo while I was there, although I have stayed there in the past. I think Key Largo is WAY overrated and certainly not as good as Marco Island. There is not as much to do in the area either unless you dive or fish (I dive). At Marco Island you get: nice beach, nice pool, spa, many GREAT seafood restaurants, nice sports activities, close to Everglades for day trip and great relaxed resort town feel. They even have a movie theater very close by. It is much more crowded until 5/1 and then slacks off.