People who use AoE daggers usually only use it in the main hand in order to get the AoE animation for both weapons. You are gimping yourself unnecessarily by using it in the offhand because one in the mainhand is all you need to get AoE for both weapons.
It is important to have high damage single-target weapon in at least the offhand because your ability damage is based upon weapon damage, and your abilities are either AoE or single-target depending upon the ability, NOT whether your weapon is AoE or single-target.
A big warning to 2handed warriors, the single-target mauls have ~10% more DPS to their AoE counterparts, but they also have ridiculously stupid targeting. You will miss 25-50% of your basic attacks with them. AoE 2handers are almost always better than single-target 2handers, unless you use abilites 95% of the time or have a very high stat single-target 2hander.