Flail of the Ages, by far. I just don't *ever* use this weapon. It's slow and always loses out in my party to more powerful weapons (and proficiencies).
After I'm done with Nalia's Keep, I rarely ever use it...
Bow of Gesen is a close second. That is the slowest friggin' bow I've ever seen and most enemies just shake off the electrical damage. I'd go with Tansheron's bow every time for a short bow.
------------------
Now where did I leave that doughnut?!