I think Exile has been developed further than Epoch for Arma 3, or at least it has recently become more popular...at least that's my experience with both mods.
Arma 3 has a new expansion called Apex coming out next week. Looks pretty sweet. In recent weeks, A3 has released several patches to lay the groundwork for Apex, and these patches seem to have improved textures, UI, and performance quite a bit.
I played an excellent Scenario with a friend for a few months called "Antistasi Altis". It's basically a turf war expansion on the Altis map - very detailed and in depth. Can be done as single player, coop, or hosted on a multiplayer server.