I think the success of the Sparkle Dun is that it sits lower in the water and therefore can be an emerger, an adult, a stillborn, etc. and if it creates a little (dragging) wake can even be an egg-laying caddis. It can be retrieved under water like a wet fly and then dried off in the false cast for another try. Thus it appeals to more trout more of the time than a more detailed/specific pattern and becomes a Universal Fly. I prefer the Sparkle Rusty Usual, but the difference between the two is minimal. Other than that, a soft hackle wet fly like a GRHE Wet is my starting point.