Faction selection question.

[Anselm]

Egyptian units are fairly unique, a good mix of armoured units with some lighter arabic desert style units. A sort of blend of lots of military styles all in one.

Anselm

[pyhhricvictory]

I liked Macedon. They have the phalanx and hoplite type infantry but in my game, I found that the archers and horsies did much better for me. They are just different enough and you get attacked from Thrace, Dacia, Greek and Romans.

Egypt is fun as well but they seem to overpower everyone else around them for quite some time.

[Jeanne d'arc]

Seleucids have a unique set of troops, especially there phalanxes beiing the ones with the longest spears in the game.They also have elephants, chariots and heavy cathaprakt cavalry.

[Basileus]

Spanish or Parthians

[Soulflame]

Well most factions have a certain diversity in units.
Carthage has the most units available behind the Romans, and some different ones too. Egypt, Pontus, Seleucids, all have a good selection and can pursue different strategies (you can make a hit and run army, a solid infantry army, or anything else you'd like).
The ones to watch out for are Gaul, Scythia, and maybe some others like Thrace and Dacia. They have a limited troop selection.

Anyway, I suggest you take a look at the guide I made (link in my sig). You can easily overview all the factions in the game and decide which faction you want. Or you can load up custom battles and try all armies out first to see which you like...