In RTW vanilla:

At start:

Mercenary Cretans -- available easiest to Greeks, Macedonians, Pontics, and Brutii assuming normal operational goals/spheres of action.

Egyptian Bowmen -- same as everyone elses generic archers for power etc, but base unit size of 120 v 80 gives them an edge (and makes them a superb garrison choice).

Scythian Horse Archers -- All H.A. are useful in the same fashion, the Scythians are just a small notch better statted.


Mid-Game:

Mercenary Cretans are still good, but they have been equalled by chosen archer warbands in Dacia, Scythia, and Germania (who fight a bit better in h-t-h as well). They are out-classed by archer auxilia (better armor and h-t-h), Pharoah's Bowmen (tough buggers these), and by Gaul's Forresters (assuming Gaul survived long enough to build them).

Among H-A, some of the Scythian Nobles are an improvement over the base model, but basic H-A never really loses its "bang-for-the-buck" value.