What sets the A3 SMG apart from other, similar weapons is its prolonged barrel. This feature makes the weapon very accurate, which is exactly what many machine guns lack.
The A3 also has the highest rate of damage among all SMGs in the game. However, keep in mind its magazine slot needs to be upgraded as it's rather limited in the vanilla version.
Taking all of this into consideration, the AUG A3 is one of the best options for both PvP and PvE in The Division 2. Everything from DPS to RPM is very well balanced here, and the gun works in various scenarios very well.