The Emerald Aisle is basically a collection of excess/surplus cars at that location of all classes (although usually not premium or large SUVs). Pretty much anyone can join EA for free. Emerald Executive Selection is a frequent renter program, you need a certain number of rentals to qualify. At MIA, the Executive Selection is along the side of the building, the Emerald Aisle is along the fence to your left.

I just went to National at MIA on Christmas Day, the Emerald Aisle was pitiful with 4 Impalas and a couple of mid-sized Chryslers. I found the manager who was on the lot, I complained about the lack of cars, and he let me get an SUV from the Executive Selection (a Chevy Equinox). Also if you ask an employee and wait around, sometimes they will refresh the Emerald Aisle with better cars. Also, be careful, veterans of National will spot and jump on a car they want. You can take the keys of a car you want and hang out for a better car.

MIA had one of the worst Emerald Aisle's I have seen, but this is a smaller National location than many I have seen also.

A Trailblazer is a pretty large SUV, you might be better off reserving if you must have this size of car (a large 3 row SUV). If you can live with a smaller SUV and risk ending up with a sedan or station wagon, you will save a lot of money at MIA by reserving a midsize car from the Emerald Aisle and getting the best vehicle you can find.

Hope this helps.