Now that I've actually found a few uniques I can weigh in on this. I've found the Spear of God, Muramasa, and Rosebud. Of these the spear is by far my favorite. It's damage is just fantastic. I don't need to couch my lance against lightly armored opponents; I can ride through a crowd of archers and one-hit them with ordinary stabs. It's also useful as a pike when facing a cavalry charge on foot or besieging a castle. If it weren't for the archers, I could eliminate an entire garrison just standing on the ladder and stabbing fools. I use the Muramasa mainly because it looks cool. It is useful as a close combat weapon when people get past my spear, but it's damage isn't as outstanding. I like Rosebud, but I don't find a stabbing sword to be a useful complement to my kit. I'd really, really like to find the Kaiserlich Cannon. I don't know how else I will succeed in besieging cities with many hundreds of defenders. I also want to find the Laurian plate because my character is Laurian.
EDIT: I just found the elephant gun today. Oh man! It's too slow to be practical in most battles, but in sieges it's the only gunpowder weapon accurate enough for me to hit archers behind cover. With this thing I was finally able to take a well-defended town for the first time instead of some dinky castle. I'm thinking of using it to snipe State troops because they never seem to charge, but that could make the fights boring. We'll see.