Nimble tasks are run by nimscript, and thus have the same limitations of the Nim VM (cannot use FFI, slow execution speed, etc).
Nake is run in pure Nim and is compiled to native code (IIRC), so if you need to use FFI or any other feature that is limited in the Nim VM, that's where you could use Nake. That said, use what makes sense for your project. For most setups, nimble + nimscript will be fine.
I use nake for non-nim project. To me, it is a cross-platform replacement of bash/python scripts.
nake provides a simple command line interface for running tasks and does not have a concept of project, no need for version, author...