I just returned from a weekend in Key Largo and chose Rainbow Reef Divers for our charter. The Good to me is a nice sized boat, good crew, fresh water rinse, fresh drinking water, and cookies. The bad to me- they pack their boats to the hilt with divers, and I don't like being amongst "21" divers when 17 of them are students......but that's just me. ;-) As already mentioned, it's very evident that they push different crew members through their op because I observed some tension amongst a couple of the hired help (the younger girls mostly). I'd use them again but probably later in the season when it's colder and not as many divers are present.
Last year I used the Florida Keys Dive Center. They are top notch in my book and will go out no matter how many divers sign up- they are in it for the enjoyment as much as they are for the money. Great people and never a bad experience. My LDS uses them solely for all of their Keys trips.