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.
Well thought out points Greg
Mine is the klinkhammer (Olive body and black hackle) , with saying that I haven’t tried the ones mentioned… Hope this thread goes on for a bit.
My ‘universal’ dry fly is either a black Chernobyle Ant, or a black Elk-Hair Caddis. If is has to be a traditional dry pattern, then it would be just a generic dry fly in either all black or all grey.
Mr Al Campbell’s SWHAPF. the first rainbow that I caught on a fly that I had tied was a SWHAPF. I immediately took the fly off and put it on my vest so that I could keep it. I was very disappointed to find it gone when I got back to the car. 
since then I have caught several fishies on those flies. 
hNt
Many years ago I ran into an old guy when I was fishing Slate Run in Pennsylvania. He was fishing a bamboo rod and working downstream. When I asked him how he was doing, he said “okay”, and told me he was using a Royal Coachman dry fly. Said that’s the only fly he ever needed, and he opened his fly box to show me its contents.
WOW! Row after row of nothing but Royal Coachmen!
In those days it wasn’t so unusual to for fishermen, even dry fly purists, to kill their catch, and Mr. Coachman was no exception. He opened his wicker creel to show me his catch and my eyes just about buggered out. In it were 4 or 5 beautiful brown trout between 14" - 16" long - very nice fish for that small stream. And I hadn’t caught a thing!
Not only did that old timer use just one fly pattern, but he told me also used to same technique for all his fishing. He always fished downstream, holding his rod high and letting the fly bounce on the water as he held it on a tight line.
Until recently it would be Gary LaFontaine’s Sparkle Pupa with a pale olive antron sheath and either peacock herl abdomen or bright green touch dubbed abdomen. As of late it would be a Klinkhammer with greenish grey body, peacock herl thorax and either Cree or Dark Barred Ginger hackle. I’m taking that this inquiry is regarding dry flies only. Lake fishing it would be a #10 peacock and black bunny Glen’s Leach it is my main searching pattern when I’m focused on Rainbow’s, which is most of the time. I almost never fish a dry fly on a lake.
Steven,
Looking in a copy of The Sportsman’s Notebook and Tap’s Tips, 4th Printing 1969 by H.G. Tapply (pgs 125-126), it seems that Mr. Tapply conspired with Harold Blaisdell (Vermont?) and Len Putnam of coastal New England to develop the Nearenuf dry fly.
Pattern: Hook - #16 and #14 mostly, with a few #12s for the Green Drake
Wings - woodduck flank tied split and upright
Hackle - mixed dark ginger and grizzly
Body - stripped peacock eye quill
Tail - two stripped grizzly hackles flared and tied extra long
One of my favorites is the Ausable Wulff, developed by Fran Betters of Wilmington N.Y. - along the west branch of the Ausable.
Best regards, Dave S.