I feel like for multi-line strings, I almost always use |, and only |. It takes the indented block as-is, which I feel like is going to be what you'd want … always?
I think maybe once, ever, I used > to fold some whitespace…?
I know the chomping & indent indicators exist, but I feel like I've only ever seen those in programmatically generated YAML. I have trouble envisioning a real-world use-case that is going to make me pull them out. They're a facet of the language that feels as if it exists solely for a processor that might need to emit any possible string, which | would not permit, and the inline strings might be uglier.
That said … there is a post like yours in every YAML thread. But I think those of us that understand YAML … I'm having a hard time grokking what you're doing that causes consternation.