It would depend on the circumstances. For a durable medical power of attorney, my youngest daughter. She sees eye-to-eye with me on end-of-life and medical emergency issues, and would do what I want her to do, even though it would be harder on her than on my other daughter or my siblings.
For financial matters, my nephew. He manages money well.
I’ve been known to bring some big friends around when I needed to get certain people to move. They didn’t have to do anything, and the guy left relatively peaceably.