Dark sword is too short and it's R2 sucks yea, Lothric Knight sword is where it's at.
I'm finally at a point where titanite chunks are flowing like water and I have a few slabs to play with, so I've been dicking around with some of greatswords/ultras and man do they just all feel like butt. My Lothric Knight sword at refined +10 is ~420 damage at 35str/40dex, meanwhile Farrons is about ~550 damage at +5, Astora Greatsword refined +10 is about 570. Murakomo is in the 520ish range at +10 sharp. The issue is though that just isn't enough damage to justify using any of it. Even at 30 endurance you only get 2-3 mega slow swings per stamina bar with the greatswords/ultras, where as the Knight sword can put out 7 in the same amount of time and still have stamina left over for a roll.
Need to find a couple more slabs to test out some of the greathammers and axes to see if maybe they bring enough damage to justify it, but so far straightswords are where it's at.