I also have this question, which brought me here. Declarative pipeline certainly seems like the preferred method and I personally find it much more readable, but I'm trying to convert a mid-level complexity Freestyle job to Declarative and I've found at least one plugin, the Build Blocker plugin, that I can't get to run even in the a script block in a step (I've tried putting the corresponding "blockOn" command everywhere with no luck, and the return error is usually "No such DSL method 'blockOn' found among steps".) So I think plugin support is a separate issue even with the script block (someone please correct me if I'm wrong in this.) I've also had to use the script block several times to get what I consider simple behaviors to work such as setting the build display name.