The only reasons why I'd think a person would dual-wield weapons is... 1) They played a lot of Demon's Souls and think they can stunlock with dual-wielded weapons (just a hint - that doesn't work anymore). 2) Two differing weapons for two different situations (or maybe even up to 4 weapons, 2 in reserve). 3) Aesthetics (for looks). 4) The weapon in their other hand is the Parrying Dagger ...
Single sword is the only weapon type I haven't tried yet outside of the intro. Kusarigama was pretty powerful but didn't seem quite as strong as dual swords. I didn't care for axes. Is there anything single swords do better than dual swords? Water weapon is so strong against bosses and windstorm seemed great for everything else. How are single swords compared to dual swords against bosses?