I think they both represent the trailing shuck and a cripple low in the film. I have found a Sparkle Dun with a synthetic shuck to do a smidge better when fishing glassy water. But once the surface is broken with movement, I give the edge to the Haystack. Not a big fan of the Comparadun wing and dry tailing. If I'm going that route I lean towards a thorax style pattern usually.

This pattern however I feel does well due to the hair attributes.