It just depends on your preference and learning style. If you like having a physical book open to read from, then buy a book. If you would rather not have a lot of things on your desk, and like reading from your screen, then study online. If you prefer more visual aids, then watching video tutorials will be better.
Figure out your preferred learning style, and go from there. Python is the same regardless of how you learn it, as long as the quality of all the sources is up to par.