What is the best weapon you can buy in elder scrolls IV oblivion

Umbra may be the most powerful weapon you can get, but you cannot buy it. Possibly the most powerful weapon you can buy is an Akaviri Warblade you can buy from Jensine which has damage of 16 and also delivers 15 pts of Damage Health and 30 points of each of Damage Fatigue and Damage Magica. It's a two-handed Longsword.