I have played as:
Romani - possibility of reenactment of "actual history", excellent for role-playing. Rather easy, very good introduction into EB (I have played S.P.Q.R. extensively on RTR Platinum before)
Macedon - recreation of the Empire of Alexander, good starting location, interesting quests (i.e. Tomb of Alexander). After a challenging start, when you have the Balkans Peninsula under your rule as well as Ionian cities, you are basically without peer competitor (AS and Ptolemaios exhausted each other, so none of them posed much of a threat in that particular campaign). Therefore I switched to
Pontus - excellent faction, challenging starting location, its best units are significantly weaker then the elites of Successors, so the challenge lasts throughout the whole campaign. You have clear objective - unify the Asia Minor, make Black Sea a Pontic lake. Diverse enemies (successors phalanxes, Armenian catphracts. sarmatian horse-archers). - If interested see my AAR here: https://forums.totalwar.org/vb/showthread.php?t=93891
That was on EB 0.81v2a with Redmeths balanced money and mercenary script.

Now I play as Pahlava on EB 1.0
- because of its brand new nomadic/pastoralism building tree
- because Arsaces has written a masterful AAR about them (The Waste Land) which brought my attention to EB in the first place
- because my previous campaigns centered on infantry, especially phalanxes, and I want to try something different
- possibility of reenactment of "actual history" (this opportunity, however, is spoiled by the stupid Bactrians who do not understand their own interest and instead of being my allies against the Seleucids, they are allied with them against me )

My next campaign would probably be the Hayasdan - because of their incredibly sophisticated reforms set, which surely will give much purpose to th gameplay.

*I have never played as "barbarian faction (for no particular reason, BTW I cannot play my "home" faction, because that would be the rebel Boii - glad to hear that they have been beefed up in EB 1.0 ).
*I do not like bordering with the edge of map (pity, Bactria will otherwise be a very interesting faction to play with)
*I do not like to manage empire I have not created myself - that rules out The Seleucids, Ptolemies and Carthage. I like those guys though.

Well, not very different from most people around here, I guess...