The reasons I think Rome is harder to play as than Carthage, on Regent...
1) I've lost as Rome twice (and not at all as anyone else in this Conquest), so I definitely have had some bad experiences with them.
2) Playing as Carthage was really easy, since Rome never made any initiatives.
3) Rome as AI against Carthage as AI never takes more than maybe a city in Spain and loses Syracuse to Carthage, so Carthage is by far better on AI.
4) In my Persia win, Carthage controlled Corsica, Sardinia, and Sicily, but at the same time had an SOD of about 30 Heavy Cavalry and several near Leptis Magna, just in case I declared war on them. Wow.
As for citizens being great for domination, that's what I thought before I lost twice. I settled the area NE of Padua with garrisons in each city, which worked great until Macedon declared war on me, with Heavy Cavalry. I concluded from that that one must either attack Celts/Gaul and focus your energy there (which AI likes to do), or go for Carthage right away. Without taking Massilia, citizens are a less useful, especially with Carthage on the Iberian Peninsula to start.
As for the war with Carthage, I think it's a lot easier for Carthage to win for three reasons:
1) Carthage has a significant amount more production power, despite their relative lack of civil defense to begin with.
2) Carthage is seafaring in a primarily island war.
3) Carthage can use Macedon to their direct advantage, while as Rome Macedon only sends a few ships to help.
All in all, Rise of Rome as Rome is HARD.