IMO , it is likely that knight is going to win in a frontal fight. Spartan uses bronze, which is heavier than iron, and they will fatigue overtime especially in a full armored battle. Both Roman and Spartan have less covering for their armor. Samurai armor are design to be flexible and more maneuverable on the battlefield, as they mainly fight on horses. Knight is the only one with full coverage iron/steel armor. Also, to point out Samurai doesn't actually uses Katana much on the battlefield but bow/arrow or spear/naginata instead, which are design to fight lighter armor infantry. While knight have traditionally carry heavy armor countering weapon such as axes or maces, as they are more used to fighting heavy armored infantry.