I know that this won’t likely be a popular opinion but I really like the MSBuild configuration way with xml and interpolation. I have found I can even reason about fairly complex configurations without too much hassle. You can also debug them which is great. It’s not that it doesn’t have its warts it’s that it really does a good job for what it’s mean to: semi-programmable configuration. It’s also extensible.
However, it is of course extremely proprietary