I prefer rot13. I don't have an extension, but I can hilight it and type "xsr13" into a terminal window which I already have open and visible. Having to visit a new webpage has higher friction, and I can't see the spoiler and its context at the same time. It's also easier for me to generate, although I don't think I ever have.

I accept that most people are probably not in the same situation. It's only minor, because If this became common I'd just write a terminal app to decode it. (The bitwise-not version is better for that: for the password version I'd have to copy link location instead of just hilighting.)