I've rented from the Miami Airport location, and the HLE on First Street and did not have a problem at either.
It was standard gold canopy service at the airport.
I'm not sure that going to one of the other locations would get you a better car, there are lots of people renting one way from the airport to the HLE's for cruises or the other way when they get back, so I'm betting the cars are pretty much shared by them all.