I wouldn't exactly call Pontos a phalanx based faction, though. More like a Persian-styled faction that has a couple phalanxes in its roster. Unlike,say Epeiros or Makedonia, one would not think of Pontos as being a faction that has an army that has to rely on phalanxes.

And Pontos really is a challenge, situated as it is on top of Arche Seleukeia. Make sure you are up to that challenge....I certainly found it far, far harder than Romani or Pahlava, don't know a thing about Getai. If you just want a traditional game with a faction that has phalanxes, Epeiros or Makedonia would probably be a better choice. If you want a totally different, very hard game, go with Pontos.

Epeiros and Makedonia are similar enough. Their early game is pretty different, which is due mostly to the famous elephants that allow for one-turn sieges as Epeiros. Makedonia's size doesn't really count for too much; I've looked at the AI Epeiros starting armies, and they look tough. Two elephant units, and plenty of phalanxes, if I recall correctly. Makedonia AI starting armies seem weaker. Especially because they sometimes end up fighting the Konion Hellion. (Not that I'd know how hard AI Epeiros is, I haven't actually played Makedonia). It's your choice when it comes to those two factions.