We have stayed at the hotel that is actually in the airport. It is very convenient, especially if your flight leaves early or you get in very late. Breakfast is included, and is quite good.

We have also stayed at the Marriott complex you mentioned, usually in the Courtyard hotel that is there. We have gotten deals before through www.simpleairportparking.com to park our car on the Marriott grounds (for less than Marriott charges and less than the airport charges). So we stay at the Courtyard, leave the car on the gated grounds, and take the Marriott shuttle back and forth to the airport.

As for the neighborhood, I suppose it is probably not the most upscale one you'll find around Miami, but it's not that bad. My wife and I have walked a couple of blocks from the hotel area to a restaurant for dinner and had no qualms about it. There are a number of decent restaurants within a very short driving distance. We will almost certainly be staying there again.