Well depends on what you are going to do really...
Cut down people without armor, the Katan's edge is sharper and would be ideal, for a well protected knight in chainmail or heavier the Katana would probably be as effective as a butterknife vs a fileīt, IE can work but would take time and considerable skill
The heavier european swords can deliver a "punch" even through armour since they are heavier. The european swords are made to last a long battle whereas the "brittle" katana is more sensitive in that regard.
It's not the size of the swords that make the outcome of the fight but the size of fight in the swordwielders.
If you take the best weapon ever made you can still be gutted by a mad fisherman with a crooked er.. knife if you don't know what you are doing.