I have not played all of the factions yet but in my opinion the Brutti seems to make the most money and they make it consistantly through out the game. The main reason for this I believe is the very easy access to Greek cities. By quickly taking all of the greek cities (including Rhodes -40% increase in naval trade) you have at your command an econimic machine that allows the Brutti to out spend, out build, and out fight any other faction on the board.
I believe Carthage would be next but they have little money to start with so it takes a little while to get ramped up to the same level as the Brutti.