YAML feels like 10 steps back; no parser I've ever used has been able to accurately give me a line number for an error, white space issues make it impossible to work with without special editor features, and some of the types are just cryptic. I spend most of my time that's spent editing configs in vim over SSH and it can be challenging at times.
TOML resolves a lot of these issues in my experience but I'd still argue that by virtue of its capability, is still quite complex when trying to define configs for new applications.