What Marriott hotels are closest to the beach in Miami or Fort Lauderdale?

I am looking for a Marriott hotel on the beach in the Miami/Fort Lauderdale vicinity. Since a few friends will be flying in without a car, we would like it to be within walking distance of the beach and some restaurants or nightlife. Additionally, it must be a Marriott or Marriott affiliate (Courtyard, Springhill Suites, Fairfield Inn) so I can use my discount. Thanks in advance!