The most versatile fly?

[namekagon]

I was wondering if anyone else has a similarly versatile fly.

Interesting question.
For terrestrials, some variation of the gurgler will cover just about anything that might fall into the water.
Even for more selective trout,,,9X out of 10 it will be good enough.

You can even go over the top and weight them.
Here's the infamous Bullhead Gurgler,,,,with just enough lead to give it slow sink properties.