The most fun I had in the first game was two-handing the Zweihander. Yes, it's slow and maybe it doesn't have the best DPS, but I love the way it pancakes enemies and just the raw strength of the weapon and how weighty the animations feel. It also makes the game more strategic and challenging, as it forces you to learn dodging and good positioning.
In the second game I used the Berserk sword instead. I forget what it's called, but it basically looks like a big slab of metal.