JSON for serialization all the way. It’s simple and to the point. It does one thing and does it well. There’s little room for annoying surprises. Any JSON can easily be minified and prettified back and forth. If you want it in binary format you can convert it to BSON.
Yaml is too much of a feature creep. It tries to do way too many things at the same time. There are so many traps to fall into if you’re not cautious enough. The same thing can be written in multitudes of ways.