Composite Excalibur (sword)
vs
Composite Mjölnir
This is strictly about the weapons, not about any specific person/character who wields them. If a wielder is needed, then assume that each wielder is identical and derives all extra abilities and powers from the weapons. Also, the issues/conditions of being worthy are turned off at this time.
A) Which weapon is more powerful overall?
B) When pitted against each other, which weapon would win the most battles?
C) Are there some locations/environments that favor one weapon or the other?
D) Which weapon would you want to bring into a fight?