The Courier is very pleasing to the eye. However, it wasn't its aesthetics that put it in AJN service, rather its capabilities. With only a crew of three, this large ship is impressively simple to operate and gives performance that was unmatched until the Quest was put into full production. The versitility of this vessel until now has been unparalleled. However, the Quest has squeezed out some models of the Courier - all E.1 and KC.2 variants were demilitarized and sold off to civilians over 10 years ago.
The Alliance ran into problems procuring Couriers directly from Imperial shipyards - the Empire felt that the Alliance was not necessarily a friendly force. Like with the Explorer, from that point the AJN's needs were fulfilled by purchasing civilian models on the open market, something the Empire could do little about (short of starting a full scale war, which fortunately they were not prepared to do on a matter this minor).
The current variants are: