Throughout the Sole Survivor will come across plenty of character who each will have their own agenda. While some in the Commonwealth might be out for themselves, there are a lot who belong to the various factions who vie for power.
As the main questline progresses, the question of which the Sole Survivor should side with in the end will arise, with each faction having its own pros and cons.
There are plenty of groups that can be met in the Commonwealth, with many having great side quests in, and some of the smaller factions have some great characters.
While there are far too many to list, some honorable mentions are the synths of Arcadia, who can be met during the DLC, the incredibly cool Atom Cats, and the recently added Enclave.
Most of the major factions can be joined, with the possibility of being a member of multiple groups, but which ones are worth the time?