The best? Well I wouldn't say there is a "best" the damage when you find it is based on your level, the type of weapon I would think however would be Daedric, strongest would prob be the Daedric 2 handed mace (Deals more damage than the other 2 but is slower.)
This game isn't like WoW. There are so many weapons, so many unique weapons, depending on when you find them determining there damage, so potentially, unless you are maxed level, you will always find a better 2 hander, no exceptions. Also your perks in 2 handed combat make a difference in there damage too.
However out of personal preference, I have always found Glass and Daedric to be pretty powerful.