Best can mean many things, but no unit is designed to do every job on the battlefield. So, it is probably better to consider each arm of the military when making such comparisons: infantry, cavalry, missiles, artillery, special forces.

Horse archers cannot defeat Spartans in the hands of a competent Greek player. They can easily take the infantry out of phalanx and rotate them as needed to keep the shield bearing on the horse archers line of fire. The horse archers will run out of arrows without having killed many Spartans or routing them. Online battles of this sort, involving many units will end up with the Greek side pressing the HAs into a corner for orderly disposal, (if the HA player doesn't just quit after running out of arrows).

But as I mentioned in the first paragraph, different arms do different jobs. Infantry isn't designed, nor expected for the most part to chase down and destroy cavalry. I think it is only fair in the rock, paper, scissors game, to compare rocks to rocks, paper to paper, etc.