Visual Studio Code is recommended, since it provides decent support for all the languages Anki uses. To set up the recommended workspace settings for VS Code, please see below.
For editing Python, PyCharm/IntelliJ's type checking/completion is a bit nicer than VS Code, but VS Code has improved considerably in a short span of time.
There are a few steps you'll want to take before you start using an IDE.
For code completion of external Python modules, you can use the venv that is
generated as part of the build process. After building Anki, the venv will be in
out/pyenv. In VS Code, use ctrl/cmd+shift+p, then 'python: select
interpreter'.
You'll need Rust to be installed, which is required as part of the build process.
Code completion partly depends on files that are generated as part of the regular build process, so for things to work correctly, use './run' or 'tools/build' prior to using code completion.
To start off with some default workspace settings that are optimized for Anki development, please head to the project root and then run:
mkdir .vscode && cd .vscode
ln -sf ../.vscode.dist/* .
Once the workspace settings are set up, open the root of the repo in VS Code to see and install a number of recommended extensions.
If you decide to use PyCharm instead of VS Code, there are somethings to be aware of.
You'll need to use File>Project Structure to tell IntelliJ that pylib/ is a sources root, so it knows references to 'anki' in aqt are valid.