What's the most powerful sword in world of warcraft

Answer 1

 [Ashbringer], the legendary blade of Alexandros Mograine.

 [Thunderfury, Blessed Blade of the Windseeker], the weapon of Thunderaan

 [Warglaive of Azzinoth] and  [Warglaive of Azzinoth], the legendary weapon set consisting of two swords, wielded by Illidan Stormrage

 [Ashkandi, Greatsword of the Brotherhood], the weapon of Anduin Lothar (speculated)

 [Glorenzelg, High-Blade of the Silver Hand], apparently stolen by Arthas and corrupted.

 [Quel'Serrar], an ancient Night elven blade.

[Quel'Delar], the reforged blade of Quel'Thalas. Obtained via a quest given by the  [Battered Hilt].

Answer 2

warglaive of azzinoth probaly.