Out of the Barbarian Invasion and the original campaigns, which did you think was better, and with which civilisation? I liked the Barbarian Invasion's better using the Huns, because you get to storm huge battlefields with thousands of horses and it is very aesthetically pleasing.
Actually I didn't play Barbarian Invasion yet. I figured that after spending so much time on the normal game I should perhaps move on to other games :)
As for the original campaigns I liked the Germans. Early in the game it is easy to defeat the AI with cheap cavalry and later you can use a mixture of Chosen Archers (long range, good armour and can melee-fight like light infantry) and Gothic Cavalry. Their war-dogs are also helpful in many situations. German infantry isn't bad either if you are on the attacking side. I also liked that their cities remain rather small, so there is less unrest and more money (for some reason cities seem to produce more moneywhen they are small). They also have some drawbacks : no siege weapons, which didn't bother me too much and many rebellious units in the woods between their cities, which is annoying but can be solved by some well-positioned diplomats later in the game. Their navy is awful, but you don't really need one anyway.
Although it had features I liked and wish were put into rome total war instead of a exp pack, I liked the orginal alot more, it simply felt like it had "more" to it.