There are plenty of active guilds on Argent Dawn. It all comes down to what you are looking for.
The PCU community has a large array of different guilds. Orgrimmar grunts of the Hand of Conquest and Stormwind guards known as Stormwind City Sentry. Mercenaries of the Sunnyglade Ratters or Red Venturers. Loyalist groups such as the Rotgarde or Grim Gest. Neutral parties such the Ebon Onslaught or Far Delvers.
List goes on and all are active.
It all depends on what you seek.
In addition, there are other guilds as well that are around, such as the Dust Devils.
So what appeals to you at this moment and we can go from there to help you look at a new character to role-play.