If you belong to Emerald Club you can either book Emerald Aisle (by booking an Intermediate size) or you can book any other size and your service will be called Emerald Reserve. With an Intermediate and Emerald Aisle, you can head over to the EA and pick anything from that aisle. There will mostly be Intermediates but sometimes they'll be an upgrade there. If you don't like what you see there, then head over to the Intermediate aisle and get one there.
If you reserve any other size (other than an Intermediate), you'll have Emerald Reserve service which means you can head to the aisle of the size you reserved...but either way (Emerald Aisle/Emerald Reserve), you will bypass the counter.
They changed Emerald Choice to Emerald Reserve on March 15. They also changed the service a bit too. Before you could book Intermediate through Full size and still have Emerald Aisle service, but not anymore. Now all sizes are Emerald Reserve except Intermediate.
Hope this helps!