This was discussed previously in this thread. A12, as I was told to book A12 when I did home based TDY, ended up being more or less a high priority standby most of the time. As in, I would be waiting to see if I had a seat right up until the door closed... even if there were unsold seats when I checked in 24 hours before. So, better than D1 but worse than A3. Someone else in this thread has indicated there is another way to book A12 that is positive space but only on select flights. That method was unavailable to me. It's still unclear that to me if 'that method' will be available to those headed to LGA. In either case, I'd consider A3 a step up from A12.