[stadeschuldt]

For a new project you definitely want to use Python 3 as Python will be EOL in 2020.

For new projects I tend to favor Python 3.7 over 3.6. But sometimes I have to fall back to 3.6 because some packages have not been updated yet and I don't want to install them from Git(Hub) (e.g. GeoPandas through pyproj).

[nerdwaller]

Another important library not supporting 3.7 is celery (distributed task queuing). Otherwise I also favor 3.7 (for contextvars and dataclasses).