I would say it's dead even between the Julii (yea I know the Romans are a little overpowered) and the Seleucids, though I'm using the Julii more now because they're just more viable. Their Cohorts take arrow fire better than Silver Shield Pikemen, and their Praetorian Cavalry are about as good as Cataphracts for less. Also, I usually end up fighting little bums that use lame factions like the Egyptians, Parthians, Scythians, or Armenians that OD on archers and horse archers, and Seleucid Pikemen fall like flies to armies like that.
Egypt is definitely my least favorite faction. I just find them way too unfair. I was once using the Julii against them once, and beat away all their Desert cavalry, which caused huge casualties against my Praetorian cavalry, which cost about twice as much, then they still have a flood of Pharoh's bowmen and Pharoh's spearmen. My Urban cohorts fight them all. I flank their Spearmen, and eventually beat them after taking most casualties from arrow fire. Now they send three more units against about 6 more units of Urbans. I end up flanking their men, and not only that, but also they're only being attacked from behind, while the enemy is shooting at a decoy unit of cavalry, but somehow their damn men can inflict more casualties on me than I can on them, even though they're the ones being attacked from behind while in phalanx formation. My men rout and the guy's 8 units of bowmen didn't even exhaust their arrows yet. A strategy that COULD NOT fail against any army with normal units gets obliterated by Egypt and their insane units. If anything their archers should be nerfed. Their regular bowmen have 120 men in a unit and their elite ones have 80 plus the same attack and defense as Principes and their cheapest cavalry has the ability to crack Praetorian Cavalry, and even causes massive damage to Cataphracts.
I put a dollar in one of those change machines. Nothing changed. ~George Carlin