if there is a dependencyScope configuration and a resolvable configuration that extends it, and I want to add another configuration that extends, is it better to extend the dependency scope or the resolvable, or what factors are there to consider when choosing?

I would say the dependencyScope, as it allows for more flexibility (the 2 resolvables can differ in what they extend from), but it depends quite a lot on the use case. Fwiw, I don't think core plugins have any configuration extending a resolvable configuration.

ok thanks!

If you want the exact same dependencies plus some more, I think it is fine to extend the resolvable. If you want a defined set that just in the default case is the same as the resolvable, extend what you want to extend from manually. As Thomas said, highly depends on the concrete use-case.