Anything big really; Axe, Hammer, Mace, something two handed & very large. Something you know is going to deal high damage. If I had to say a number one favorite fantasized weapon, I'd say a really large gigantic Scythe.
As someone who got official bokken training, I must say swords are pretty darn heavy (even wooden ones). I've held a few katanas and longswords, and they are a lot more difficult to use than they look. That said, I'd probably use some sort of two-handed sword, just because it's all I am mildly proficient with.