Try Boudica of Ethiopia. Alternatively, any Aggressive civ of Ethiopia.
Seriously, with just 5XP from the city (4 if Cha), you can build Drill 4 Combat 1 Oromo Warriors.
-On top of their promotions, these guys are also immune to first strikes.
-If for some reason you don't have pikemen, you can use the 2 promotions to make a C2 D2 Formation Oromo, which has defense strength 13.05 plus any terrain defense. Even C3 knights cannot get greater than 37% odds against these. Still, it'd always be better to be defending using pikes.
-Importantly, they can be upgraded to any other unit in their upgrade path and retain these promotions. Imagine having a huge bunch of D4 C1 infantry (with only 4XP each), freshly upgraded straight after you reach Assembly Line, or the same units as riflemen the moment you reach Rifling. If you are attacking cities, it's even worth keepking the oromo's around for their immunity to first strikes, when attacking weakened defenders that still have first strikes.
The Ethiopian UB is also solid, allowing easier cultural victories - something easier to achieve with such a highly promoted military too.
The main thing you'd need bo make sure to do is have your economy set up so that you can get a bunch of gold for the upgrades quickly. Perhaps by running merchants in GP Farm for a great merchant, or running a cottage-heavy economy so you can send the science slider to 0% for a few turns.