Without considering your playstyle/abilities and looks:
Knightly Arming Sword - by far.
Hmm...I always measure a weapons usefulness by 4 catagories. Length, damage, speed, and special abilities (or x-factor). The very scientific measurements I use are the following ratings (from worst to best): Worst, Poor, Fair, Good, Great, Best.
Knightly Arming Sword:
Length: Best
Damage: Fair
Speed: Fair
Special: none
Langes Messer:
Length: Good
Damage: Good
Speed: Good
Special: none
Langes is more "balanced". Knightly has the advantage of reach.
You guys like my rating system?