Greatsword is stronger but weighs 12.0 more units and it's WA, while devastating, is predictable and easily to avoid. Charge can rollcatch and other stuff, just don't walk into a parry.
The notes recommend chaos, but I don't. Dark supposedly deals more damage to living enemies (like other players). Also, fire resistance scales with strength, but dark doesn't, so against any build with str, you'll deal more damage going Dark. It also synergizes better with a dark sorcery build (use the dark clutch ring and the izalith staff)