Define "one fly"
I would choose a PTN because I can dress it small, large, long, short, with beads, without beads, with hot spots, with sparkle, with a wing and more.
Is that still "one fly"?
I have them large to represent stoneflies, but also with a pearly thorax that, when stripped, looks like a minnow. I have them dressed with a CDC plume to act as an emerger, I have them ties curved to look like a buzzer, of course I have beads to get them down in the river....the list is endless.