If I understand it correctly, Emerald Choice is similar to Emerald Aisle service in that you bypass the counter and go directly to where the cars are located. However instead of picking any car off of the Emerald Aisle with Emerald Aisle service, you go directly to the aisle where the specific kind of car you reserved is located. For example if you reserved a minivan you go to the minivan aisle and pick any vehicle out of that aisle. Same with Premium or Luxury aisle, depending on whatever class you reserved. You still get to pick your own car, and you don't need to go to the counter. You just get to pick the class you specifically reserved in that exact aisle, as opposed to whatever is available in the Emerald Aisle.