Emerald Aisle & Emerald Choice are both only available to Emerald Club members and both allow you to skip the counter and go straight to the garage, with the paperwork done at the checkout booth as you drive out. If you are not an Emerald Club member, you have to go to the counter inside the airport and stand in line, but you will still have the choice of the size aisle you reserved (if you reserved a van, you can pick out of what's available in the van aisle). The advantage to Emerald Choice is skipping the counter.