BUHAHAHAHAHAAHAHAHA! Even though I hate the historical inacuracy of calling them Numedian (Carthage in located in the current capital of Tusina, or however you spell it) I'm a Carthage to the death fan and constantly use them in the Ancient and even into the middle ages. It's like getting a bowman and hoplite in the same unit (acutally, it's exactly like that lolz). It's with these guys that I don't fear legions, hoplites, bowmen, and to an extent knights/samuari/war elephants/riders. Although, I have to say I voted for Immortals. While cav are a bit annoying becuase they tend to pop out of fog of war at the worst possible times, attack, and then retreat, Immortals are just plain scary for two reasons.
1. They're the most powerul Ancient Times unit in the game
2. they're defense allows them to defend against most offensive units until Pikemen
This is part of the reason i refuse to play at Perisa anymore. Too overpowered. I see those coming and even with my mercs, I'm still like "aw ****. I'm screwed." this is probabblly why I stay nice with them until my war age, industrial.
edit: I love the merc animation by the way. They reach very far out, and with a downward motion. It's like "I'm stabbing you straight throught the neck, and I'm slashing you in half *****!"