as siegfriedfr already pointed out Carthage and the ptolemies are the easiest factions whereas Romans are maybe even easier from a battle and finance Point of view, they are a bit confusing concerning recruitment and reforms. reading the FAQ and some guids on this board will help you with that.
and I'd like to say that bactria is far more threatend than Lusotania in the early game but when the worst is over probably one of the most potent factions.
furthermore the "barbarian" starting postitions also differ a lot in dificulty:
Casse cannot/will not be conquered by anyone on m/m no matter how stupid you manage your troops ;)
Sweboz and Getai get slightly off statring positions thus have some time to develop until they are attacked.
Aedui and Areveni get attacked from the beginning
that said Sweboz have the worst economy, getai the widest troop selection and Casse have "funny" (because chariot mounted) generals-> worthless for many players the secret weapon for those who are able to control them.
ps:and sewers and low level temples- build roads/farms/market
and for Epeiros and Koinon Hellenon It can be profitable to first transfer some troops and THEN disband the last navy(eg the KH army on Kreta)- disband your fleets on turn one (except if you play carthage, you'll need it)
Bookmarks