multi element dual swords are a gimmick rly, for the best possible choice use full element
only exception is maybe the kirin DS which does Para n Lightning o_o;;;
in other words, for efficiency use full element
however if ur more versed in DS u might find urself finding the twin nails more useful *shrug* i usually prioritize my Main weapon class before others even if the other has a better element choice for the material(besides its not like u cant get more) o_o;