[quote=Reaper]
Actually, it depends. Soldiers are taught to fight in a unit. Which means their martial training is heavily focused on not killing the guy beside you as well. If Guardians fight in smaller groups or alone, then they'd be better at one-on-one fights.This argument is pointless. Spies with bows, poison and daggers make armour useless. :D
[/quote]

You are absolutely right, bows, daggers and poison make armor useless :P

And for the training of Guardians, I guess it depends on how you were trained and by whom. Nyirr, for example, has been brought to fight in the war against Malfear and since then has always worked as a group and never alone or a duo. Nyirr isn't so great in one vs one because of his inherent training in larger groups of at least 4-5 people. 

Kotori, on the other hand, was trained to protect her Mage and defend him as best as she can, which means she has an easier time coordinating with one or two teammates and defeating a smaller group of people efficiently.

(PS: It is what I see, I might be wrong)