My brother and I go to Key Largo for a week every year (except for last year, obviously), and we will be there starting July 17th. We always stay at the Courtyard (next to the Marriott), and will be using RRDC during that week. We really like RRDC as we have always had good experiences with them. Yes, you do get plenty of people on their boats. We love the fact that they provide a dive guide with every dive. This gives us a "stress" free dive vacation without having to pay for the guide service. We can just dive, and not worry about navigating areas we are not familiar with. We always stay in the back of the dive group, but always within sight of the guide. This allows us an easy dive without the other divers getting to close to us, but still able to communicate with the guide if/when need be. We have used other shops in the area, and have had bad experiences with them. Like others have mentioned, there are plenty of restaurants near those two hotels along with grocery store, drug store, and even a Diver's Direct next door to the Marriott in case you need new gear, or get something fixed.
How are you planning on getting to Key Largo without a car? Miami is the nearest airport, and its almost 1.5 hours away from Key Largo. Key West also has an airport, but it is around 2.5 hours from Key Largo.