`python3 -m venv venv` will use whichever minor version of Python 3 that `python3` currently points to. If you are working on multiple projects that span different Python 3 minor versions, pyenv makes the process of switching between versions much easier. You would activate the specific version you need with pyenv then use `python -m venv venv` to create the virtual environment using that specific version. It's not one or the other, but they work nicely together.