Eagle Warrior (Aztec) - 28
Hetairoi (Macedon/Alexander) - 21
Legion (Rome) - 5
Mamluk (Arabia) - 31 (34 - 3) There's nothing wrong with this unit, but it does appear later than the other remaining units, and as such will not influence the early game to the same degree.
Pítati Archer (Nubia) - 46 (45 + 1) Still the best unique unit. With regards to an earlier comment about how it stacks up in combat to the other Ancient Era UU's which are left: I believe the Pitati has the edge. For one thing, its effective base cost is 47, compared to 65 for the Eagle Warrior and 55 for the War-Cart. That means you get 7 Pitatis for every 5 Eagles, or every 6 War-Carts, which is a small advantage for the Pitati. Strength is pretty much the same for all three. When it comes to speed, it is very hard for an Eagle Warrior to even get to strike at a Pitati before getting destroyed. With the War-Cart, it is a closer competition, as it is fast enough to keep up with and even overrun the Pitati. In the situation where you have 1 War-Cart vs 1 Pitati Archer, and mostly open terrain, I believe the War-Cart will win many of the times. Still, I believe the Pitati wins most of the times in a real battle where there are more units in the field, because of range. While melee units can only attack the 6 hexes adjacent to them, ranged units have up to 18 hexes available. This makes it a lot easier to focus fire, without sacrificing position, giving it a clear tactical advantage. Furthermore, the range means that Pitati Archers don't take any damage when they strike. It also means it is possible to attack safely while protected either by a city, or other units. Finally, the Pitati synergizes with Nubia's increased experience gain for ranged units. Just by being a ranged unit which can reach more tiles means it will be able to strike more frequently (and without taking damage), earning it more experience than the melee units. On top of that, +50% for belonging to Nubia. More experience means additional combat strength, as well as heals in combat.
War Cart (Sumer) - 36