python3 -m pip install VS pip3 install

I would advise against ever calling any pip somecommand (or pip3) script directly. Instead it's much safer to call pip's executable module for a specific Python interpreter explicitly, something of the form path/to/pythonX.Y -m pip somecommand.

There are many advantages to this, for example:

• It is explicit for which Python interpreter the projects will be pip-installed (Python 2 or 3, inside the virtual environment or not, etc.)
• For a virtual environment, one can pip-install (or do other things) without activating it: path/to/venv/bin/python -m pip install SomeProject
• Under Windows this is the only to safely upgrade pip itself path\to\venv\Scripts\python.exe -m pip install --upgrade pip

But yes, if all is perfectly setup, then python3 -m pip install SomeProject and pip3 install SomeProject should do the exact same thing, but there are way too many cases where there is an issue with the setup and things don't work as expected and users get confused (as shown by the many questions about this topic on this platform).

References

• Brett Cannon's article "Why you should use python -m pip"
• pip's documentation section on "Upgrading pip"
• venv's documentation section on "Creating virtual environments": "You don’t specifically need to activate an environment [...]"

It's the same thing.

python3 -m pip install calls pip as a module in python, while pip install calls pip directly.

The only reason to prefer the first is that in order to use the second you need to have set pip in your environmental variables (for Windows). In older versions of python this was not done automatically during installation, rather you had to do this manually. That's why in a lot of guides you might see them using the first syntax for their instructions (because it works always, as long as you have python3 in your environmental variables. For Linux/Mac operating systems there isn't any difference.