I'd probably take the RC Key Biscayne if I wanted to be quiet and relaxed. If you want to let the kids have fun themselves I'd consider the Biltmore in Coral Gables. It's not on the beach but is beautiful, has great food and service and has the country's largest swimming pool, not to mention a nice golf course. It is also far closer to variety than are the others.

Still, all of those are very nice hotels. They just have different favor, that's all.