Most likely the Hellenistic factions offer a lot of combat. I played DEI with Nabetea, and it takes a very long time to get started before you can start your engine and shove your armies to the map. There's also other factions as well. So the Greek factions which can be done will offer a lot more variety.
I'd say save the Eastern factions for later, Parthia, Nabetea, Pontus.
I wouldn't mind one Barbarian faction being available for release.
Just my opinion!