i usually fish streams and small rivers in the sierra of california and like today, will catch browns, as well as rainbows (and brook in other places) on top with standard dries. royal wulffs, para adams, BWOs, humpies, para black ants, and my fave an elk hair caddis or other variations of dry caddis flies. for bigger browns, i go deeper with subsurface flies, not dries... though in the fall have landed big browns on small dries.
My most productive is probably a Griffith's Gnat
Lately, I've been prospecting almost exclusively with a Royal Coachman and have been doing very well.
But my favorite has to be the Usual
Buggy, high floater, no hackle, one single material.
Could be a mayfly, could be a terrestrial....covers a lot of bases
I've thought about what makes a favorite fly a favorite fly for me, and it comes down to the materials. I tie a few variations of a brown deer hair caddis using coastal deer hair, and I would have to choose this as my top dry for trout in general.
I think the deer hair is the key here for many top water flies- which I would call "variations of deer hair," including the caddis, humpies, sparkle duns, hairwing duns, wulffs, stoneflies, and hoppers, etc.
Now, of course, there's grizzly and brown hackle, which are also used in many of the flies mentioned above, so it's hard to factor these out, especially when you think of a fly as effective as an Adams. If I had to choose a favorite hackle, I would pick the grizzly.
This brings me to my second favorite fly (not that you asked)- the Griffith's Gnat. Again, it's really a favorite in terms of material, because I think of many other flies, including the adams, parachutes, and some nymphs and even some buggers as a "variation of hackle."
Just some food for thought. Sorry for the long-winded nature of my response.