If this topic is not restricted to the European theatre, then I would say the samurai are the most effective infantry. The katana was a prolific killer of men, superbly forged by folding the iron millions of times over. The blades were of better quality than even those created by the legendary swordsmiths at Toledo.

Unlike the knights of europe, the Japanese also respected archers. The samurai were trained not only with the katana but also many took on archery, and were skilled in both sword and bow. Their dedication and fighting spirit was second to none.

However, like the knights of europe, the samurai were obsessed with personal honour, and this was a major problem for them. In civil war, such as plagued Japanese history, this was not such a problem. But when foreign armies invaded, such as the Mongols, their discipline and lack of honour meant they were more proficient as a unit than their samurai enemies.