Uncompyle6 works for Python 3.x and 2.7 - recommended option as it's most recent tool, aiming to unify earlier forks and focusing on automated unit testing. The GitHub page has more details.
With these tools, you get your code back including variable names and docstrings, but without the comments.
The older Uncompyle2 supports Python 2.7 only. This worked well for me some time ago to decompile the .pyc bytecode into .py, whereas unpyclib crashed with an exception.