You're probably asking the wrong kind of question, a better question might be who was the best trained. There's no objective way of determining who was the "best" as different factors will give varying results. For example: Terrain, Commanders, Tactics and the enemy will have a large effect on the supposed effectiveness of a unit. Where one unit might have done spectacularly, another might have failed but different circumstances will provide different results. So yeah, there's no way to find a "best" unit objectively. Better questions might be: "best trained troops" or "Most effective battles"