There are many Courtyard by Marriott hotels in the Miami area. Which one in particular? If you stay at one in Miami Beach it is just 4 or 5 or so miles to the port.
There can be advantages to being a little further from the port, like fewer passengers in your hotel vying for taxis. We stayed at the Hyatt Regency in Coral Gables prior to our cruise on the Freedom. Not much around there at night to do, and we used a limo service, but when we checked out cruise morning we were the only ones at the curb and there were several available taxis along with our limo waiting. Got to the ship in about 20 minutes.