I would have to say if I had one fly right now in the Rockies it's a "modified sparkling dun". Tied in different sizes and colors. Good low riding mayfly emerger. I like to tie them kinda sloppy but they really seem to work well.
I like to try different patterns, for searching for trout. Big dries are by far the most fun so in the fall its most likely a pink pookie in different colors.
Royal wulff like Lee says "its like cheese cake after a meal" I break out this fly when fish just won't take any thing else when feeding on top. Seems to always land a few fish. Kind of my last resort fly, not cause it's bad it's just that kinda fly for me. I prefer the split wing version over the parachute too. I caught my second ever greyling in a rare location on one.