This is just my personal opinion, but I think YAML is more intuitive but has a lot more footguns and gotchas, while TOML is more consistent but less obvious (ironically, given the name.)

This may contribute to YAML's popularity in CI systems, because CI systems often need to be adjusted by someone who isn't super familiar with the syntax, and YAML is easier to intuit than TOML.

TOML is much simpler in general but it does have its warts. It's basically just key = "value" pairs in [sections] for the simple stuff.

I think it's saner, but still has some bizarre design choices