The raid instance Battle of Dazar'Alor has separate instance for the Horde and the Alliance, since they kind of tell their own story of the raid. Both entrances are super accessible for tough.
The Alliance entrance to Dazar'Alor is on the docks in Bolarus, not far away from where you sign up for Island Expeditions.
The Horde entrance to Dazar'Alor is next to Zacalo in Zuldazar.
So both factions can enter the raid instance from their own hubs, making it the easiest raid to enter!