Using pip vs. MacPorts for installing Python packages
You should use pip because it's the Python-native tool for managing package installations but you shouldn't pip-install things into your base Python installation. It can be a mess to have to sort out fixed version dependencies between multiple software repositories if you're pip-installing everything into your base Python installation on your machine.

Instead, you should pip-install virtualenv and then use it to manage different, virtual Python installations and all the associated pip-installed packages packages for each virtual environment.

This allows you to switch from working with, say, beautifulsoup 1.x in one software repository to beautifulsoup 2.x in another repository without having to wade through dependency management hell.