If possible, prefer what tools in your vicinity use. My team uses Kubernetes and Concourse extensively, which both use YAML, so I tend to stick with YAML since

If possible, prefer what tools in your vicinity use. My team uses Kubernetes and Concourse extensively, which both use YAML, so I tend to stick with YAML since people are already familiar with it. (More recently, I've come around to prefer plain environment variables for configuration, but that only works nicely when the amount of configuration is fairly limited, say 20 values instead of 1000 values.) For my own use, I do prefer TOML.